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2May5&4 


Mutants  and  Hybrids  of  the  Oenotheras. 


BY 


D.  T.  MACDOUGAL 


ASSISTED  BY 


A.  M.  Vail,  G.  H.  Shull  and  J.  K.  Small 


WASHINGTON,  D.  C. : 
Published  by  the  Carnegie  Institution  of  Washington 

1905 


Carnegie  Institution  of  Washington,  Publication  No.  24, 


Papers  of  Station  for  Experimental  Evolution  at 
Cold  Spring  Harbor,  New  York.    No.  2. 


PRESS    OF 

HENRY    E.  WILKENS    PRINTING    CO. 

WASHINGTON,   D.   C. 


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Mutants  and  Hybrids  of  the  Oenotheras 


BY  D.  T.  MACDOUGAL 
ASSISTED  BY  A.  M.   VAIL,  G.   H.  SHULL,t  AND  J.  K.  SMALL 


PURPOSE  AND  SCOPE  OF  INVESTIGATIONS. 

The  more  important  features  of  the  investigations  of  De  Vries  in 
which  lines  of  descent  were  seen  to  originate,  which  embodied  new 
qualities  and  groupings  of  characters,  constant  and  fully  transmissible, 
are  now  so  familiar  to  all  naturalists  that  no  rehearsal  is  necessary  in 
the  present  paper.  Early  in  1902  the  senior  author  received  seeds  of 
the  Lamarck's  evening-primrose,  and  these,  with  seeds  of  various 
species  obtained  directly  from  their  native  habitats  in  North  America, 
were  cultivated  in  the  New  York  Botanical  Garden,  in  which  the  con- 
ditions of  soil  and  climate  are,  of  course,  widely  different  from  those 
of  the  botanical  garden  at  Amsterdam,  Holland. 

Among  other  primary  purposes  of  the  cultures  it  was  deemed  of 
great  importance  that  the  mutants  should  be  tested  as  to  their  stability 
when  grown  as  biennials  after  the  predominant  habit  of  the  genus. 
The  results  of  this  test,  together  with  detailed  descriptions  of  three  of 
the  mutants,  have  already  been  given  in  an  article  in  which  occasion 
was  taken  to  set  forth  briefly  the  principal  tenets  of  the  mutation  theory 
as  propounded  by  De  Vries  (MacDougal,  1903).  It  was  found  that 
the  mutant  forms  were  not  only  physiologically  differentiated,  but  were 
also  easily  separable  from  one  another  and  from  the  parental  type  when 
tested  by  accepted  taxonomic  criteria,  and  by  an  examination  of  the 
features  of  their  life-histories.  Furthermore,  all  the  forms  came  true 
to  their  newly  assumed  groupings  of  characters  without  reversions,  and 


*T'he  contents  of  this  paper  were  presented  before  the  weekly  botanical  con- 
vention at  the  New  York  Botanical  Garden,  October  19,  1904. 

fOf  the  staff  of  the  Station  for  Experimental  Evolution  of  the  Carnegie 
Institution  of  Washington,  Cold  Spring  Harbor,  Long   Island,  N.  V. 


Library 
N.  C.  State   College 


4  MUTANTS   AND    HYBRIDS    OF   THE    OENOTHERAS. 

exhibited  only  fluctuating  variations  of  ordinary  amplitude,  although 
the  last-named  feature  was  not  examined  by  statistical  methods.  An 
investigation  of  this  feature  is  described  in  the  present  paper. 

During  the  earlier  cultures,  plans  were  formulated  for  a  somewhat 
inclusive  investigation  of  the  genetic  relationships  of  the  various 
members  of  the  genus,  and  of  the  variations,  or  mutations,  which 
might  be  found  to  occur  in  O.  lamarckiana  in  America,  and  in  the 
other  species  of  the  group.  To  this  end  correspondence  was  estab- 
lished with  collectors  in  various  parts  of  America  and  Europe,  and 
material  was  obtained  from  such  distant  points  as  New  Zealand, 
Mexico,  Holland,  and  Japan.  A  supply  of  paraffined  paper  bags  was 
furnished  by  Professor  De  Vries,  and  later  those  manufactured  for  the 
Station  for  Experimental  Evolution  at  Cold  Spring  Harbor  were  used 
for  inclosing  the  inflorescences,  by  which  absolutely  pure  crops  of 
seeds  of  the  species,  as  well  as  of  the  various  hybrids,  were  obtained. 
All  sowings  of  seeds  were  made  in  soil  sterilized  in  an  autoclav  for 
three  or  four  hours.  A  number  of  the  parcels  of  earth  treated  in  this 
manner  were  moistened  and  kept  under  proper  conditions,  but  in  no 
instance  were  any  germinations  of  other  Oenotheras  seen.  In  order  to 
economize  time  it  was  found  most  convenient  to  grow  the  evening- 
primroses  as  annuals,  which  may  be  done  by  germinating  the  seeds  in 
a  propagating  house  and  then  transplanting  them  to  the  experimental 
grounds  early  in  May.  The  earlier  cultures  were  begun  about  Jan- 
uary i ,  but  it  was  found  that  ample  time  for  the  entire  development  of 
the  plant  was  obtained  if  the  sowings  were  made  late  in  February  or 
early  in  March. 

The  portions  of  the  general  investigation  in  which  such  progress 
has  been  made  as  to  warrant  the  publication  of  the  present  paper  are 
as  follows : 

(i)  Determination  of  the  ancestral  habitat  and  dissemination  of 
0?iagra  {Oenothera)  lamarckiana . 

(2)  Description  of  such  species  of  Onagra  {Oenothera}  as  have 
been  kept  under  cultivation  for  one  or  two  seasons  in  order  to  facili- 
tate observation  of  possible  mutants. 

(3)  Analysis  of  the  relationship  between  0.  lamarckiana  and 
other  species  of  the  genus  by  means  of  hybridizations. 

(4)  Estimation  of  the  dominance  of  parental  characters  in  hybrids 
of  0.   lamarckiana  X  0.  biennis  and  0 .  lamarckiana  X  0.  cruciata. 

(5)  Determination  of  the  recurrence  and  stability  of  mutants  of 
the  Oenotheras  ;  description  of  0.  gigas  as  cultivated  in  the  New 
York  Botanical  Garden. 

(6)  Estimation  of  the  fluctuating  variability  of  some  of  the  char- 
acters of  0 .  lamarckiana^  0.  nanella,  and  O.  rubrinervis. 


PLATE   II. 


Large-flowered  Evening  Primrose,  figured  in  Barton's  Flora  of  North  America, 


resembling  Onagra  lamarckiana. 


MUTANTS    AND    HYBRIDS   OF    THE   OENOTHERAS.  5 

DERIVATION  OF  ONAGRA  (OENOTHERA)  EAMARCKIANA. 

As  a  result  of  the  earlier  examination  of  material  in  a  few  her- 
baria in  Europe  and  America  no  specimens  of  O.  latnarckiana  were 
found  that  had  been  grown  in  America,  and  it  was  suggested  that  it 
might  have  been  originally  native  to  a  restricted  range  in  Virginia 
from  which  it  had  been  exterminated.  The  inquiry  upon  this  phase 
of  the  investigation  has  been  continued  however,  with  the  result  that 
many  historical  records,  as  well  as  some  fairly  well  authenticated 
material,  have  been  found. 

Barton  (1821)  describes  an  Oenothera  under  the  name  of  O. 
grandiflora  in  his  Flora  of  North  America,  which,  with  the  accom- 
panying plate,  well  represents  O.  latnarckiana.  (PI.  II.)  This  plant 
is  described  as  "  native  in  the  woods  and  fields,  and  about  habi- 
tations, in  Carolina  and  Georgia,  flowering  from  May  to  August." 
The  fact  is  recalled  by  Barton  that  Elliott  restricted  the  habitat  of  this 
form  "to  the  vicinity  of  habitations  in  South  Carolina  and  Georgia, 
remarking  that  it  is  certainly  not  indigenous  in  the  low  country." 

Pursh  (1814)  had  previously  described  an  O.  grandiflora  similar 
to  that  mentioned  by  Bartram,  as  "in  woods  and  fields  of  Carolina," 
and  with  ' '  flowers  larger  than  any  other  of  the  North  American 
species,  and  of  an  agreeable  scent." 

The  Floral  Magazine  for  1862  gives  a  plate  of  Oenothera  lamarck- 
iana  with  some  notes  on  the  species  from  which  the  following  is 
quoted:  The  one  now  figured  was  grown  by  Messrs.  Carter  &  Co., 
the  well-known  seedsmen  of  High  Holborn  and  of  the  Crystal  Palace 
nursery,  Forest  Hill.  To  them  we  are  indebted  for  the  following- 
particulars  (Dombrain,  1862): 

We  received,  about  four  years  ago,  some  seed  from  Texas  unnamed.  When 
we  had  flowered  it  we  sent  some  blooms  to  Dr.  LJndley,  who  pronounced  it  to  be 
Oenothera  latnarckiana,  a  species  we  believe  introduced  into  England  by  Mr. 
Drummond.  Its  height  is  between  3  and  4  feet;  it  blooms  the  first  year,  is  a 
very  hardy  biennial,  and  is  superior  to  any  other  Oenothera  in  the  size  and  num- 
ber of  its  blossoms,  which  measure  4  inches  in  diameter. 

A  reproduction  of  the  same  plate  is  to  be  found  in  L,'  Illustration 
Horticole  for  1862,  together  with  a  discussion  of  the  origin  and  rela- 
tionships of  the  various  species  and  a  citation  of  the  statements  quoted 
above.     (Leniaire,  1862.) 

A  specimen  in  the  Gray  Herbarium  of  Harvard  University  was 
examined  which  agrees  perfectly  with  O.  latnarckiana.  From  the 
inscription,  which  is  in  Dr.  Asa  Gray's  handwriting,  it  appears  that 
this  plant  was  grown  from  seed  in  the  botanical  garden  at  Cambridge, 
Mass.,  in  1862.     The  sheet  also  bears  the  note,  ' '  Said  by  English  hor- 


6  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

ticulturists  to  come  from  Texas,"  and  also  "Oe.  lamarckiana ,"  all  by 
Dr.  Gray.  It  is  to  be  noted  that  the  date  of  the  above  culture  agrees 
with  that  of  the  Drummond  plants  in  England  mentioned  above. 

The  second  phase  of  the  effort  to  trace  O.  lamarckiana  to  its 
original  habitat  was  directed  to  an  examination  of  the  material  to  be 
found  in  the  American  herbaria  and  to  excursions  to  some  of  the  his- 
torical locations.  Several  specimens  of  prime  interest  were  encoun- 
tered. A  specimen  collected  by  A.  W.  Chapman  in  Florida,  and  sent 
by  him  to  Europe,  becoming  a  part  of  the  Meissner  herbarium  which 
was  afterward  purchased  by  Columbia  University,  was  thought  by 
Professor  De  Vries  to  be  0.  lamarckiana,  and  the  mark  on  the  sheet 
shows  that  it  was  used  by  Chapman  (i860,  1872,  1884)  in  making  up 
the  description  of  O.  bie?inis  in  the  editions  of  his  southern  flora,  in 
which  O .  grandiflora  Ait.  was  given  as  a  synonym  in  the  editions  of 
i860  and  1862,  but  does  not  appear  in  the  later  edition  of  1897.  In 
the  description  he  says  :  ' '  Varies  greatly  in  pubescence  and  size  of 
flower,"  while  the  habitat  is  given  as  "Fields  and  waste  places." 
The  elimination  of  the  synonym  from  the  last  edition  of  the  book  can 
not  be  accounted  for,  although  the  plant  was  presumably  growing  in 
a  wild  condition.  A  duplicate  of  the  specimen  mentioned  above  is 
reported  by  Mr.  CD.  Beadle  to  be  in  the  Biltmore  Herbarium  at 
Biltmore,  N.  C.  A  similar  specimen  is  to  be  found  in  the  herbarium 
of  the  Missouri  Botanical  Garden. 

During  the  visit  of  Professor  De  Vries  to  America  in  the  summer 
of  1904  he  joined  in  the  quest  for  specimens  of  O.  lamarckiana  and 
called  attention  to  a  sheet  of  material  in  the  herbarium  of  the  Phila- 
delphia Academy  of  Sciences,  collected  by  C.  W.  Short  near  Lexington, 
Ky.,  which  he  considered  as  0.  lamarckiana,  and  which  was  grown 
wild  in  the  locality  recorded. 

The  co-operation  of  a  number  of  botanists  in  various  parts  of  the 
supposed  range  of  the  species  was  secured  and  a  thorough  search  was 
made  in  the  vicinity  of  Nashville,  Tenn.,  by  Prof.  Geo.  A.  Martin  ; 
in  the  vicinity  of  Knoxville,  Tenn.,  by  Prof.  S.  M.  Bain;  in  the 
vicinity  of  Lexington,  Ky.,  by  Prof.  H.  Garman  ;  and  in  the  vicinity 
of  Courtney,  Mo.,  by  Mr.  B.  F.  Bush.  Up  to  the  present  time,  how- 
ever, no  living  plants  have  been  found  that  might  be  included  within 
the  descriptions  of  0.  lamarckiana. 

The  above  evidence  makes  it  fairly  conclusive,  however,  that  the 
large-flowered  evening-primose  which  formed  the  basal  material  for 
the  experimental  researches  of  De  Vries  is,  or  was,  a  component  part 
of  the  flora  of  North  America  and  has  been  seen  in  the  Carolinas, 
Florida,  Kentucky,  and  Texas  during  the  last  century,  and  that 
material    Irom    Texas    examined    by    Ljndley   fairly   represents   the 


MUTANTS    AND    HYBRIDS   OF   THE    OENOTHERAS.  J 

species.  The  main  line  of  descent  has  endured  practically  unchanged 
for  a  period  of  116  years  in  European  gardens,  and  was  first  observed 
to  exhibit  mutations  resulting  in  the  production  of  new  elementary 
species  as  early  as  1887,  although  but  little  doubt  exists  that  this  was 
by  no  means  the  beginning  of  its  period  of  mutability. 

REDISCOVERY  OF  O.  GRANDIFLORA  (AiT.)  Vail  IN  AMERICA. 

During  the  course  of  the  investigation  of  the  records  it  became 
evident  that  one  or  more  large-flowered  evening-primroses  not  recog- 
nized in  local  floras  had  been  found  in  southern  United  States  at 
various  times.  One  of  the  most  interesting  of  these  discoveries  was 
that  of  Bartram  referring  to  a  locality  on  the  east  bank  of  the  Alabama 
River  above  Mobile  and  between  that  place  and  the  junction  of  the 
Alabama  and  Tombigbee  rivers.     He  says  : 

Early  one  morning,  passing  along  by  some  old  uncultivated  fields,  a  few  miles 
above  Taensa,  I  was  struck  with  surprise  at  the  appearance  of  a  blooming  plant, 
gilded  with  the  richest  golden  yellow ;  stepping  on  shore,  I  discovered  it  to  be  a 
new  species  of  the  Oenothera  (Oenothera  grandiflora,  caule  erecto,  ramoso, 
piloso,  7,  8  pedalis,  ioliis  semi-amplexi-caulibus,  lanceolatis,  serratodentatis,  flori- 
bus  magnis,  fulgidis,  sessilibus,  capsulis  cylindricis,  4  angulis,)  perhaps  the 
most  pompous  and  brilliant  herbaceous  plant  yet  known  to  exist.  It  is  an  annual 
or  biennial,  rising  erect  seven  or  eight  feet,  branching  on  all  sides'  from  near  the 
earth  upwards,  the  lower  branches  extensive,  and  the  succeeding  gradually  shorter 
to  the  top  of  the  plant,  'forming  a  pyramid  in  figure ;  the  leaves  are  of  a  broad 
lanceolate  shape,  dentated  or  deeply  serrated,  terminating  with  a  slender  point, 
and  of  a  deep  full  green  color;  the  large  slender  flowers  that  so  ornament  this 
plant,  are  of  a  splendid  perfect  yellow  color;  but  when  they  contract  again  before 
they  drop  off,  the  underside  of  the  petals  next  the  calyx  becomes  of  a  reddish 
flesh-color,  inclining  to  vermilion;  the  flowers  begin  to  open  in  the  evening,  are 
fully  expanded  during  the  night,  and  are  in  their  beauty  next  morning,  but  close 
and  wither  before  noon.  There  is  a  daily  profuse  succession  for  many  weeks, 
and  one  single  plant  at  the  same  instant  presents  to  view  many  hundred  flowers. 
I  have  measured  these  flowers  above  five  inches  in  diameter;  they  have  an  agree- 
able scent. 

After  leaving  these  splendid  fields  of  the  golden  Oenothera,  I  passed  by  old 
deserted  plantations  and  high  forests,  etc. 

Bartram 's  expedition  was  undertaken  "At  the  request  of  Dr. 
Fothergill,  of  L,ondon,  to  search  the  Floridas  and  the  western  parts 
of  Carolina  and  Georgia,  for  the  discovery  of  rare  and  useful  products 
of  nature,  chiefly  in  the  vegetable  kingdom.  In  April,  1773,  I 
embarked  for  Charleston,  South  Carolina,  on  board  the  brigantine, 
Charleston  Packet ,  Captain  Wright , "  etc .  (Bartram ,  1 793 ,  pp .  404-405 . ) 

Seeds  of  the  above  plant  were  evidently  sent  to  Fothergill,  and 
the  following  is  the  original  description  of  the  plant  by  Aiton,  made 
from  specimens  grown  at  Kevv.  He  says  "grandiflora  2.  Oe.  foliis 
ovato-lanceolatis,   staniinibus   declinatis,   caule    fruticoso,    L, '  Herit. 


8  MUTANTS   AND    HYBRIDS    OF   THE    OENOTHERAS. 

V 

stirp.  nov.  Tom.  2.  tab.  4.  Great-flowered  Oenothera,  Nat.' of  North 
America.  Introd.  1778  by  John  Fothergill,  M.  D.  Fl.  July  and 
August"     (Aiton,  1879). 

It  being  deemed  very  important  that  a  visit  to  the  locality  men- 
tioned by  Bartram  should  be  made,  Prof.  S.  M.  Tracy,  of  Biloxi, 
Miss.,  generously  undertook  to  make  the  search.  In  accordance  with 
arrangements  he  proceeded  up  the  Alabama  River  on  August  16,  1904, 
and  five  days  later  came  upon  the  plant  not  far  from  the  original 
locality.     Professor  Tracy  has  kindly  prepared  the  following  report  : 

The  locality  for  this  plant,  as  given  by  Bartram,  was  "  a  few  miles  above 
Taensa."  The  country  immediately  about  Ten  saw  is  mostly  the  dry,  pine  hills 
common  in  that  section,  and  a  careful  search  for  several  miles  about  the  town 
did  not  reveal  a  single  plant  belonging  to  the  Epilobiacese.  Fort  Mimms,  5  miles 
from  Tensaw  on  the  bank  of  the  Alabama  River,  was  doubtless  Bartram's  head- 
quarters while  he  was  in  that  part  of  the  State,  but  a  careful  search  of  the  river 
for  some  miles  failed  of  results.  Dixie  Landing,  25  miles  above  Fort  Mimms  by 
river,  and  13  by  road  from  Tensaw,  was  the  first  place  where  the  plant  was  seen. 
Immediately  below  the  steamboat  landing  there  is  quite  a  stretch  of  abandoned 
fields  covered  with  a  dense  growth  of  Chamaecrista  robasta  from  4  to  5  feet  in 
height,  and  those  plants  are  thoroughly  tangled  with  Bradburya  virginiana,  which 
makes  walking  exceedingly  difficult.  The  evening-primrose  was  found  as  an  occa- 
sional plant  in  this  growth,  the  first  plants  being  seen  about  a  quarter  of  a  mile 
below  the  landing,  and  others  being  found  more  or  Less  abundantly  for  more  than 
a  mile  down  the  river.  When  growing  in  the  thick  weeds  the  plants  were  mostly 
erect,  with  simple  stems,  a  few  of  which  were  beginning  to  branch  at  the  top.  A 
few  plants  were  found  immediately  on  the  river  bank,  and  even  on  the  sides  of 
the  almost  perpendicular  bank,  which  is  about  20  feet  high,  and  when  growing  in 
that  location  were,  as  Bartram  describes  them,  "  Rising  erect  7  or  8  feet,  branch- 
ing on  all  sides  from  near  the  earth  upwards,  the  lower  branches  extensive,  and 
the  succeeding  gradually  shorter  to  the  top  of  the  plant,  forming  a  pyramid  in 
figure."  The  largest  plant  -found  measured  8  feet  9  inches  in  height.  No  small 
plants  were  found,  and  from  the  root  and  stem  characters  the  plant  is  doubtless 
an  annual.  No  plants  were  found  more  than  200  yards  from  the  bank  of  the 
river,  and  only  a  few  plants  were  found  in  the  shade  of  trees.  Hundreds  of 
plants  were  examined,  but  no  mature  seed  could  be  found. 

A  visit  to  Earle's  Landing,  5  miles  below  Dixie  Landing,  showed  the  plant 
to  be  fairly  abundant  there  also.  In  nearly  all  cases  they  grew  on  alluvial  soil, 
which  was  sandy  rather  than  heavy,  and  none  was  found  near  wet  or  marshy  places. 
The  river  bank  was  examined  nearly  the  whole  of  the  distance  from  Dixie  to 
Earle's  Landing,  and  the  plant  was  not  rare  on  open  ground  covered  with  Chamae- 
crista, but  was  not  seen  in  any  other  location.  All  of  the  region  examined  was  on 
the  east  bank  of  the  Alabama  River.  A  gentleman  owning  land  immediately 
opposite  Dixie  informed  me  that  it  grew  in  one  place  on  the  west  bank. 

A  large  number  of  herbarium  specimens  we're  prepared  by  Pro- 
fessor Tracy,  all  of  which  were  forwarded  to  the  New  York  Botanical 
Garden  for  examination,  and  from  which  seeds  were  obtained  suitable 
for  cultures  which  promise  to  be  of  great  service  in  comparisons  with 
the  other  large-flowered  species  of  the  evening-primroses. 


Ill—       111. 


Fig.  i.     Rosette  of  Onagra  biennis  five  months  old. 


Fig.  2.     Rosette  of  Onagra  cruciata  five  months  old. 


MUTANTS   AND    HYBRIDS   OF    THE    OENOTHERAS.  Q 

ONAGRA  (OENOTHERA)  BIENNIS  (E.)  Scop. 

Many  collectors  and  taxonomists  include  a  number  of  elementary 
species  in  Onctgra  biennis  and  attribute  to  it  an  extremely  wide  range 
of  fluctuating  variability.  On  the  other  hand,  workers  who  have 
carried  on  cultural  experiments  with  individuals  representing  a  typical 
elementary  species  describe  it  as  fluctuating  between  very  narrow  limits. 
The  actual  inclusion  of  the  species  is  not  so  important,  in  connection 
with  the  present  investigation,  as  the  degree  of  constancy  of  the  various 
strains  grouped  around  the  species  and  sometimes  included  in  it. 

In  order  to  carry  on  observations  on  these  points,  and  upon  "  the 
changes  produced  by  cultivation,"  upon  which  some  systematists  lay 
so  much  stress,  a  number  of  plants  of  0.  biennis  (in  the  strictest  sense), 
growing  in  uncultivated  land  in  the  New  York  Botanical  Garden  in 
1903,  were  selected  to  form  the  basis  of  a  pedigree-culture  in  1904. 
Seeds  were  duly  harvested  at  the  end  of  the  season  and  sown  in  the 
propagating  house  early  in  January.  The  plautlets  were  transferred 
to  the  experimental  grounds  late  in  May  and  began  to  bloom  early  in 
July.  The  species  was  thus  grown  as  an  annual  during  a  season  of 
about  nine  months  in  soil  rich  with  fertilizers.  Furthermore,  the 
individuals  were  placed  in  rows,  over  a  meter  apart,  and  were  kept  free 
from  the  competition  of  weeds.  Briefly  stated,  it  may  be  said  that  in 
no  single  feature,  nor  in  any  instance,  did  these  plants  transgress  the 
measurements,  or  show  different  forms  of  organs,  from  those  of  wild 
specimens  in  the  vicinity.  The  size  of  the  leaves,  the  amount  of  the 
pubescence,  the  size  of  the  flowers  and  capsules,  and  the  formation  of 
the  branches  are  capable  of  modification  by  soil-moisture,  humidity, 
intensity  of  illumination,  and  competition,  as  in  thousands  of  other 
well-defined  species,  but  these  modifications  did  not  bring  the  species 
nearer  in  aggregate  character  to  any  of  the  closely  allied  forms.  Exact 
records  and  observations  were  kept  during  the  entire  life-histories  of 
the  individuals,  by  the  aid  of  which  the  following  description  has 
been  prepared  : 

Seedling  about  hvo  months  old. — Leaves  nearly  glabrous  ;  blades 
oval  to  oblong-oval,  the  larger  ones  about  10  mm.  wide,  obtuse  at  the 
apex,  each  rather  gradually  narrowed  into  a  petiole  (fig.  1). 

Seedling  five  months  old. — Rosette  open  ;  leaves  rather  copiously 
fine-pubescent;  blades  oblong  to  elliptic,  the  larger  ones  fully  2.5  cm. 
wide,  quite  approximately  repand-denticulate,  with  the  teeth  more 
pronounced  at  the  base,  acute  at  the  apex,  each  narrowed  into  a  short 
petiole.      (PI.  Ill,  fig.  1.) 

Matitre  rosette. — Leaves  ample,  rather  copiously  fine-pubescent, 
the  larger  ones  about  27  cm.  long,  6  to  7  cm.  wide  ;  blades  oblong  to 


10 


MUTANTS   AND    HYBRIDS    OF    THE   OENOTHERAS. 


elliptic,  or  slightly  broadened  upwards,  unevenly  repand-denticulate 
and  mostly  rather  jagged-toothed  near  the  base,  the  petioles  relatively 
stout. 

Adult  plant  (Pis,  IV  and  V). — Plant  luxuriant,  mostly  i  meter 
tall,  or  less.  Stem  slightly  uneven,  but  scarcely  channeled,  hirsute, 
with  spreading-ascending  somewhat  rigid  hairs,  copiously  branched 
throughout,  the  lower  branches  decumbent,  the  upper  ones  spreading 
or  curved  upward  ;*  leaves  very  numerous,  1.5  to  2  dm.  long  near  the 

base  of  the  stem  ;  blades 
elliptic-oblanceolate  to 
elliptic-lanceolate; 
shallowly  but  rather 
prominently  toothed, 
and     often    jagged- 
toothed  near  the  base, 
acuminate,  those  of  the 
upper   cauline   leaves 
mostly  elliptic,  acute,  sessile,  or  nearly 
so;  bracts  mainly  lanceolate,  narrowed 
or  rounded  at  the  base  ;    conic  por-  ■ 
tion  of  the  bud  14  to   18  mm.  Ions-, 
finely  pubescent,  the  free  tips  of  the 
sepals  about  2  mm.  long  ;  hypanthium 
2  to  3  cm.  long,  5  to   6  mm.  wide  at 
the    mouth,   nearly  terete,   sparingly 
pubescent  or  glabrate  ;  sepals  15  to 
20  mm.  long,  much  shorter  than  the 
tubular  portion  of  the  hypanthium, 
petals  rather  delicate,  12  to  16  mm. 
truncate  or  slightly  emarginate  at  the  apex;  filaments  8  to  10 
long;  anthers  7  to  8  mm.  long  ;  pistil  shorter  than  the  stamens  ; 
stigmas  4  to  5  mm.  long;  capsule  3  to  3.5  cm.  long,  7  to  7.5  mm.  in 
diameter  at  the  thickest    point,   finely    pubescent,   slightly  curved, 
markedly  narrowed  at  the  apex.  (PI.  VI.) 

It  is  to  be  seen  from  the  above  description  that  O.  biennis  is 
capable  of  self-fertilization  by  reason  of  the  superior  length  of  the 
stamens,  a  fact  that  was  demonstrated  in  the  experimental  grounds. 
To  secure  purely  fertilized  seeds  it  was  only  necessary  to  inclose  the 
inflorescence  in  a  parchment  bag  during  the  opening  of  the  flowers. 

*Plants  growing  in  thickets  are  more  spindling  and  have  the  lower  branches 
suppressed,  while  the  young  rosettes  are  luxuriant,  with  broader  leaves  under 
such  circumstances. 


*ig.  1.- 


-Onagra  biennis  seedling  three 
months  after  germination. 


the  free  tips  4  to  5  mm.  long 


long, 
mm. 


PLATE   IV. 


Onagra  biennis,  wild  specimen,  grown  in  competition  with  other  meadow  plants. 


PLATE   V. 


MUTANTS    AND    HYBRIDS   OF    THE    OENOTHERAS.  II 

After  an  examination  of  material  in  the  field  in  America  in  the 
summer  of  1904,  Professor  De  Vries  informs  the  authors  that  the 
O.  biennis  used  in  his  breeding  experiments  at  Amsterdam  differs  from 
the  foregoing,  and  is  to  be  included  with  a  form  usually  termed 
O.  biennis  grandifiora  by  collectors.  The  exact  relationship  of  the 
two  has  not  yet  been  carefully  determined. 

ONAGRA  ARGILLICOLA  Mackenzie. 

Within  the  last  year  a  new  wild  species  of  evening-primrose  has 
been  brought  to  notice  from  the  mountains  of  Virginia  and  West  Vir- 
ginia, being  described  by  Mr.  K.  K.  MacKenzie  as  "  one  of  the  most 
noticeable  and  common  plants  on  the  line  of  the  Chesapeake  and  Ohio 
Railroad  on  both  sides  of  the  boundary  line  between  Virginia  and 
West  Virginia."  It  has  also  been  collected  by  Mrs.  L.  F.  Ward,  at 
"Alleghany,"  W.  Va.,  and  by  Mr.  and  Mrs.  E.  S.  Steele  at  Sweet 
Springs,  W.  Va.,  and  the  cultures  in  the  New  York  Botanical  Garden 
were  begun  with  seeds  from  the  latter  locality.  The  following  descrip- 
tion has  been  compiled  from  observations  on  living  plants  of  the 
resultant  cultures  : 

Seedling  about  two  months  old. — Leaves  minutely  pubescent,  copi- 
ously so  near  the  base  ;  blades  oblong  or  elliptic-oblong,  the  larger 
ones  less  than  1  cm.  wide,  obtuse,  each  gradually  narrowed  into  a 
copiously  pubescent  petiole. 

Seedling  five  months  old. —  Rosette  relatively  lax  ;  leaves  minutely 
pubescent;  blades  spatulate  to  narrowly  linear-spatulate,  the  larger 
ones  over  25  cm.  long,  2  to  2.5  cm.  wide,  repand,  more  distantly  so 
and  with  more  pronounced  teeth  near  the  base,  each  gradually  nar- 
rowed into  a  long  petiole. 

Mature  rosette. — Leaves  numerous  and  conspicuously  elongated  ; 
glabrous,  or  nearly  so,  except  the  sparingly  ciliate  margins,  the  larger 
ones  over  40  cm.  long,  2  to  2.5  cm.  wide  ;  blades  broadly  linear  to 
linear-spatulate,  sinuate,  the  teeth  slightly  more  pronounced  near  the 
base;  petioles  relatively  stout. 

Adult  plant. — Plant  rather  luxuriant,  depressed  in  habit.  Stems 
suppressed  or  very  short,  the  branches  radiate,  decumbent,  not  chan- 
nelled, somewhat  tortuous,  mainly  6  to  12  dm.  long,  puberulent  and 
pubescent,  with  few  spreading  or  ascending  hairs;  leaves  very  numerous, 
10  to  15  cm.  long  on  the  lower  part  of  the  branches  ;  blades  undulate, 
or  repand-denticulate,  those  on  the  lower  part  of  the  branches  broadly 
linear  to  narrowly  linear-oblong,  acute  or  short-acuminate,  each  nar- 
rowed into  a  semi-terete  petiole,  those  of  the  upper  cauline  leaves 
similar  to  those  of  the  lower,  but  relatively  shorter  and  broader,  and 


12  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

sometimes  inclined  to  be  linear-lanceolate,  sessile  or  short-petioled  ; 
bracts  lanceolate,  truncate  at  the  base,  shorter  than  the  hypanthium  ; 
conic  portion  of  the  bud  about  4  cm.  long,  glabrous,  the  free  tips  of 
the  sepals  subulate,  approximate  at  the  base,  but  ascending  ;  hypan- 
thium 4  to  5  cm.  long,  about  6  mm.  wide  at  the  mouth,  ridged,  gla- 
brous ;  sepals  34  to  47  mm.  long,  shorter  than  the  tubular  portion  of 
the  hypanthium,  the  free  tips  about  6  mm.  long  ;  petals  rather  firm, 
4  to  4.5  cm.  long,  truncate  or  broadly  emarginate  at  the  apex ;  fila- 
ments 21  to  23  mm.  long  ;  anthers  12  to  13  mm.  long  ;  capsule  2.5  to 
3  cm.  long,  about  7  mm.  in  diameter  at  the  thickest,  point,  glabrous, 
strongly  curved,  narrowed  from  the  base  to  the  apex.     (PI.  VII.) 

0.  argillicola  is  to  be  distinguished  by  the  fact  that  it  is  well 
adapted  to  securing  cross-fertilization.  When  the  flower-buds  come 
to  the  morning  of  the  day  on  the  evening  of  which  they  will  open,  the 
pistil  takes  on  a  greatly  accelerated  rate  of  growth  and  pushes  out  of 
the  flower-buds  to  a  length  of  3  or  4  mm.,  bearing  the  unfolded  stig- 
mas in  a  position  in  which  they  may  readily  receive  pollen  carried  by 
the  wind  from  neighboring  flowers.  It  is  not  actually  known ,  however, 
whether  pollination  is  secured  in  this  manner,  or  whether  insects  are 
of  some  aid  in  the  matter.  A  similar  behavior  of  0.  lamarckiana 
near  the  close  of  the  season  is  reported  in  Holland.  The  decumbent 
or  non-ascendant  branches  of  0.  argillicola  form  a  dense  cluster  which 
gives  it  a  very  striking  appearance.  The  main  bud  of  the  central 
stem  appears  to  remain  dormant. 

The  great  size  of  the  flower  of  this  species  doubtless  accounts  for 
some  of  the  reports  of  the  presence  of  0.  grandMora  in  the  Virginias 
and  Pennsylvania,  while  the  habit  of  the  plant  may  have  also  sug- 
gested some  of  the  notions  prevalent  as  to  the  variability  of  0.  biennis, 
with  which  it  may  have  been  confused. 

ONAGRA  CRUCIATA  (NuTT.)  Small. 

A  number  of  roots  and  some  seeds  of  0.  cruciata  were  obtained 
from  Sandy  Hill,  N.  Y.,  near  L,ake  George,  at  the  close  of  the  season 
of  1902,  and  early  in  the  spring  of  1903  were  divided  into  two  por- 
tions, one  of  which  was  sent  to  Professor  De  Vries  at  Amsterdam, 
Holland.  Only  about  a  dozen  plants  were  brought  to  maturity  in  the 
New  York  Botanical  Garden  during  1903,  attention  being  directed 
principally  to  the  observations  on  0.  lamarckiana  and  its  mutants. 

A  letter  was  received  from  Professor  De  Vries  under  date  of  Sep- 
tember 19,  1903,  in  which  he  said  : 

Until  a  few  -weeks  ago,  and  before  flowering,  the  plants  were  a  very  uniform 
lot,  with  the  characteristic  reddish  crowns  and  nutating  tops.  But  now  they  are 
no  longer  uniform.     There  are  two  very   distinct  types,  only   differing   in  the 


PLATE   VI. 


1  Vy      3  U  ~      5 

Onagra  biennis. 

leaf  from  young  rosette;  2,  leaf  from  rosette  four  months  old;  3,  leaf  from  lower  part  of  mature 
rosette;  4,  leaf  from  upper  part  of  mature  rosette;  5,  stem-leaf;  6,  bract;  7,  unopened  bud; 
8,  flower  with  petals  removed;  9,  petals  of  maximum  size;  10,  mature  capsule.  1  to  5,  one-half 
natural  size  ;  6  to  10,  natural  size. 


PLATE  VII. 


y, 


A 

/ 


Onagra  argillicola. 

i,  2,  leaves  of  young  rosette  ;  3,  leaf  from  adult  rosette  ;  4,  stem-leaf  ;  5,  flower  with  petals  removed  ; 
6,  bract;  7,  flower-bud;  8,  flower-bud  immediately  previous  to  opening,  with  stigma  exposed; 
9,  petal ;  10,  capsule.   1  to  4,  one-half  natural  size  ;   5  to  10,  natural  size. 


PLATE    VI 


MUTANTS   AND    HYBRIDS    OF   THE   OENOTHERAS.  1 3 

flowers  and  flower-buds.  Both  types  are  to  be  found  in  the  plants  coming  from 
the  seeds,  as  well  as  in  those  grown  from  the  roots  you  sent  me.  The  differences 
are  slight,  but  striking,  absolutely  individual,  and  without  transitions.  Most  of 
the  individuals  have  broader  linear  petals  and  comparatively  more  rounded 
flower-buds.  The  others  have  narrower  and  therefore  more  strictly  linear 
petals,  and  thicker  buds. 

I  have  also  sown  seed  I  got  from  Prof.  B.  L.  Robinson,  of  Harvard  Univer- 
sity, gathered  at  Jeffrey,  N.  H.,  under  the  name  of  O.  cruciata.  They  are  wholly 
different'  from  yours,  being  more  slender,  less  nutating,  and  with  a  strikingly 
longer  calyx-tube. 

The  same  facts  are  given  in  ' '  Species  and  Varieties  :  Their  Origin 
by  Mutation  "  (De  Vries,  1905,  p.  589),  in  which  it  is  also  stated  that 
"  It  seems  not  improbable  that  0.  cruciata  includes  a  group  of  lesser 
unities,  and  might  soon  prove  to  comprise  a  swarm  of  elementary 
species,  while  the  original  strain  might  even  now  be  in  a  condition  of 
mutability." 

The  cultures  of  1904  included  over  sixty  specimens  of  0.  cruciata 
which  reached  the  adult  stage,  and  included  not  only  the  two  forms 
which  he  had  observed  to  arise  from  the  seeds  and  roots  sent  him  from 
this  place,  but  also  the  third  obtained  only  from  material  from  New 
Hampshire.  It  is  obvious,  therefore,  that  one  form  arises  spontane- 
ously from  one  of  the  other  two  forms  suddenly,  and  dried  specimens 
from  the  crop  of  1903  in  the  New  York  Botanical  Garden  show  that 
it  originated  in  this  manner  here  in  the  first  year  of  cultivation, 
although  the  second  half  of  the  same  lot  of  seeds  sent  to  Professor  De 
Vries  failed  to  give  rise  to  it  in  Amsterdam. 

The  evidence  at  hand  therefore  seems  to  confirm  the  suggestion 
as  to  the  mutability  of  the  species,  but  nothing  may  be  said  as  to  which 
of  the  types  constitutes  the  parent.  The  characters  of  the  forms  are 
as  follows : 

No.  1  (PI.  VIII)  .—Adult  plant  robust  and  luxuriant.  Stem  1  to 
1.5  meters  tall,  copiously  branched,  the  branches  spreading,  sparingly 
hirsute,  the  hairs  rather  ascending,  1.5  to  2.5  dm.  long  on  the  lower 
part  of  the  stem  ;  blades  narrowly  spatulate,  finely  toothed  near  the 
apex,  coarsely  and  somewhat  doubly  toothed  below  the  middle,  each 
narrowed  into  a  short  semi-terete  petiole,  those  of  the  upper  cauline 
leaves  oblong-lanceolate  to  lanceolate,  sessile,  all  more  or  less  pubes- 
cent about  the  veins  beneath  ;  bracts  oblong-lanceolate,  about  one-half 
as  long  as  the  hypanthium,  truncate  at  the  base  ;  conic  portion  of  the 
buds  slender,  16  mm.  long,  or  somewhat  longer,  sparingly  pubescent, 
the  free  tips  of  the  sepals  4.5  to  5  mm.  long;  hypanthium  slender 
terete  or  nearly  so,  30  or  32  mm.  long,  becoming  glabrous,  about  4  mm 
wide  at  the  mouth  ;  sepals  17  to  20  mm.  long,  linear-lanceolate,  about 


14  MUTANTS   AND    HYBRIDS    OF    THE    OENOTHERAS. 

one-half  as  long  as  the  tubular  portion  of  the  hypanthium,  the  free 
tips  4  mm.  long;  petals  delicate,  linear  or  nearly  so,  10  to  15  mm. 
long,  obtuse  ;  filament  9  to  10  mm.  long  ;  anthers  about  5  mm.  long  ; 
style  shorter  than  the  stamens  ;  stigmas  about  4  mm.  long  ;  capsules  2 
to  2.5  cm.  long,  6  to  7  mm.  in  diameter  at  the  thickest  point,  nearly 
glabrous,  mainly  longer  than  the  bracts.     (PL  IX,  fig.  1.) 

This  form  included  about  52  of  the  individuals  grown  during 
1904.     The  other  two  forms  may  be  characterized  as  follows  : 

No.  2. — Bracts  broadly  lanceolate  or  ovate-lanceolate,  round- 
truncate  at  the  base,  about  as  long  as  the  hypanthium  ;  conic  portion 
of  the  bud  sparingly  pubescent,  15  mm.  long  or  less;  hypanthium 
stoutish,  nearly  terete,  28  to  30  mm.  long,  sparingly  pubescent, 
abruptly  dilated  at  the  top,  and  about  5  mm.  wide  at  the  mouth  ; 
sepals  14  to  15  mm.  long,  linear-lanceolate,  about  one-half  as  long  as 
the  tubular  portion  of  the  hypanthium,  the  free  tips  about  5  mm. 
long;  petals  firm,  broadly  linear  or  linear-oblong,  8.5  to  10  mm. 
long,  obtuse;  filaments  8  to  9  mm.  long;  anthers  6  mm.  long;  style 
shorter  than  the  stamens;  stigmas  6  mm.  long;  capsules  2.5  to  3  cm. 
long,  7  to  8  mm.  in  diameter  at  the  thickest  point,  with  few  scattered 
hairs,  slightly  curved,  narrowed  to  the  apex.  (PL  IX,  fig.  2.)  Seven 
individuals  of  this  type  were  found  in  the  cultures. 

No.  3. — Bracts  oblong  or  ovate-oblong,  narrowed  at  the  base, 
shorter  than  the  ovary  or  slightly  longer  ;  conic  portion  of  the  buds 
stout,  9  to  1 1  mm.  long,  with  few  scattered  short  hairs;  hypanthium 
slightly  ribbed,  stoutish,  25  to  27  mm.  long,  becoming  glabrous,  rather 
gradually  dilated  at  the  top  and  about  4  mm.  wide  at  the  mouth;  sepals 
9  to  10  mm.  long,  much  less  than  one-half  as  long  as  the  tubular 
portion  of  the  hypanthium,  the  free  tips  3  to  3.5  mm.  long;  petals 
broadly  linear-oblong,  6  or  7  mm.  long,  obtuse ;  filaments  6  mm.  long; 
anthers  4  mm.  long;  style  shorter  than  the  stamens;  stigmas  3  mm. 
long;  capsules  about  2.5  cm.  long,  7  to  8  mm.  in  diameter  at  the 
thickest  point,  with  few  scattered  hairs,  slightly  curved,  narrowed  to 
the  apex.  (PL  IX,  fig.  3.)  Six  individuals  were  seen,  all  of  which 
completed  their  seasonal  development  much  earlier  than  the  other 
two  forms. 

In  the  observations  made  during  the  earlier  part  of  the  develop- 
ment of  the  plants  nothing  was  recorded  by  which  the  three  forms 
might  be  distinguished,  and  hence  the  following  characters  may  be 
taken  to  apply  to  the  entire  lot,  although  it  is  probable  that  most  of 
the  descriptions  were  made  from  mutant  individuals. 

Seedling  abotd  two  months  old. — Leaves  very  sparingly  pubescent; 
blades  oblong,  elliptic  or  oval,  the  larger  ones  8  to   11   mm.  wide, 


PLATE   IX. 


Onagra  cruciata :    Buds,  bracts,  capsules,  flowers,  and  petals  of  the  three 
elementary  forms.    Natural  size. 


PLATE  X. 


Onagra  cruciata. 

leaf  from  young  rosette  ;  2,  leaf  from  lower  part  of  mature  rosette  ;  3,  leaf  from  upper  part  of 
mature  rosette;  4,  stem-leaf ;  5,  rosette  five  months  old  ;  6,  rosette  two  months  old  ;  7,  rosette 
nearly  five  months  old,  with  narrower  leaves.    1  to  4,  half  natural  size;  5  to  7,  natural  size. 


MUTANTS   AND    HYBRIDS   OF   THE    OENOTHERAS.  1 5 

undulate,  obtuse  or  merely  acutish  at  the  apex,  each  rather  gradually 
narrowed  into  a  petiole.     (PI.  X,  fig.  6.) 

Seedlings  five  months  old. — Rosettes  not  dense ;  leaves  glabrous  or 
nearly  so,  except  the  ciliate  margins;  blades  spatulate,  some  of  them 
narrowly  so,  the  larger  ones  2  to  2.5  cm.  wide,  shallowly  repand-dentic- 
ulate,  mostly  acute,  as  long  as  the  petioles  or  longer.    (PL  III,  fig.  2.) 

Mature  rosette. — Leaves  conspicuously  elongated,  obscurely  fine- 
pubesdent,  the  larger  ones  about  26  cm.  long,  25  to  30  mm.  wide; 
blades  narrowly  spatulate,  repand-dentate,  more  distantly  so  and  with 
prominent  teeth  near  the  base,  petioles  relatively  slender. 

All  of  the  forms  included  in,  and  arising  from,  0.  crucial  a  are 
capable  of  self-fertilization  when  the  inflorescences  are  inclosed  in 
bags.  So  far  as  present  information  goes  the  species  of  the  evening- 
primroses  native  to  northeastern  America  may  be  said  to  have  compar- 
atively small  flowers  and  to  be  capable  of  self-fertilization,  although 
visited  frequently  by  flying  insects.  The  species  ranging  to  the  south- 
ward have  larger  flowers,  and  by  reason  of  the  superior  length  of  the 
pistils  are  adapted  to  cross-fertilization,  although  it  is  not  definitely 
known  that  self-fertilization  does  not  ensue.  In  0.  argillicola  the  early 
protrusion  of  the  stigmatic  surfaces  from  the  unopened  flower-bud 
has  the  appearance  of  a  positive  adaptation  for  securing  pollen  from 
other  flowers,  by  the  agency  of  wind,  gravity,  or  insects. 

HYBRIDS. 

Among  the  crosses  made  in  the  New  York  Botanical  Garden 
during  1903,  that  of  0.  lamarckiana  X  0.  cruciata  and  the  reciprocal 
were  attempted.  The  first  only  was  successful,  as  the  castration  of 
the  flowers  of  0.  cruciata  was  not  accomplished  sufficiently  early  to 
prevent  self-fertilization.  Likewise  the  removal  of  the  stamens  of 
0.  lajiiarckiaua  was  not  done  in  such  manner  as  to  exclude  the  action 
of  its  own  pollen  and  the  pistil-parent  appeared  as  a  pure  strain  in  the 
cultures. 

0.  lamarckiana  X  0.  cruciata. — A  detailed  study  of  the  hybrids 
obtained  by  the  pollination  of  0.  lamarckiana  by  0.  cruciata  was  made 
by  De  Vries,  but  the  pollen-parent  was  evidently  a  highly  variable 
hybrid  race  which  bore  the  general  vegetative  characters  of  the 
true  cruciata,  but  which  showed  a  fluctuating  variability  in  its  flowers, 
from  an  atavistic  obcordate  form  of  petal  to  others  of  the  slender 
cruciata  type.  The  form  in  question  is  known  in  Europe  as  Oeno- 
thera cruciata  varia  and  is  held  by  De  Vries  to  be  probably  a  hybrid  of 
0.  maricata  and  cruciata.     (De  Vries,  1903,  pp.  100-110,  593_633-) 


l6  MUTANTS   AND    HYBRIDS   OF   THE    OENOTHERAS. 

The  individuals  of  the  hybrid  as  made  in  the  New  York  Botanical 
Garden  in  1903  were  seen  to  be  furnished  with  narrower  leaves  in  the 
earliest  stage  of  the  seedlings,  all  of  which  but  one  were  destroyed  by 
insects  before  the  main  axis  was  formed.  The  plant  was  recognizable 
at  some  distance  throughout  its  entire  existence  by  its  light  yellowish- 
green  color.  The  leaves  of  the  young  rosettes  were  ovate-lanceolate, 
obscurely  and  remotely  repand-denticulate,  blunt  at  the  apex,  with  the 
laminae  extending  down  the  petioles  to  the  bases  in  the  form  of  wings 
1  to  2  mm.  in  width.     (Plate  XII.) 

The  leaves  of  the  mature  rosette  were  narrowly  lanceolate-oblong, 
being  broadest  above  the  middle  and  tapering  to  both  ends,  with  the 
petioles  winged.  The  laminae  were  approximately  denticulate  in  the 
apical  portion  and  irregularly  so  in  the  basal  half.  All  of  the  leaves 
of  the  rosette  and  stem  were  minutely  pubescent. 

The  stem  attained  a  height  of  about  55  cm.  and  bore  a  number 
of  short,  spreading  branches  arising  from  the  base  of  the  main  stem 
and  reaching  half  of  its  length.  Numerous  shorter  branches  arose 
from  the  entire  stem  from  a  short  distance  above  the  base.  The 
apical  portions  of  all  branches  were  tinged  with  red.  The  stem  leaves 
were  narrowly  oblong-lanceolate,  tapering  to  both  ends  and  acute  at 
both  ends;  9  to  11  cm.  long,  and  14  to  17  mm.  wide.  The  terminal 
rosettes  were  dense,  close,  symmetrical,  and  spreading.  The  first 
flower  was  shown  on  August  12,  about  six  weeks  later  than  the  begin- 
ning of  the  blooming  of  either  parent. 

The  petals  were  recurved  after  the  manner  of  0.  cniciata  and  were 
from  9  to  1 1  mm.  long,  varying  from  linear-oblong  to  irregularly 
obcordate  or  truncate,  being  entire,  obscurely  emarginate  or  irregu- 
larly notched  near  the  apex.  Furthermore,  these  various  forms  might 
be  illustrated  in  a  single  flower  (see  Plate  XII,  figs.  6a,  ya,  and  8). 
The  definite  tips  of  the  calyx-segments  were  spreading  in  the  bud  and 
were  3  to  15  mm.  long.  The  stamens  varied  in  length,  being 
shorter  than  the  pistils  in  some  flowers,  and  longer  in  others.  The 
ovaries  were  about  9  mm.  long,  slightly  hirsute,  and  the  hypanthium 
was  glabrous.  The  bracts  were  lanceolate-acuminate.  The  calyx- 
segments  were  much  shorter  than  the  hypanthium.  The  hypanthium 
showed  a  purplish  tinge  and  the  petals  were  flesh-color,  except  at  the 
tips.  The  capsules  were  rounded,  obscurely  angled,  20  mm.  long 
and  4  to  5  mm.  in  thickness,  tapering  from  near  the  base  to  the  tip, 
and  bearing  a  few  spreading  hairs.     (PI.  X.) 

This  hybrid  agrees  quite  well  with  0.  critciata  varia  as  described 
by  De  Vries,  which  he  thought  was  a  hybrid  between  muricata  and 
cruciata.     Whether  it  is  actually  identical  with  this  form  can  not  be 


PLATE   XI 


,:^.. 


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'jH* 


Adult  specimen  of  the  hybrid  Onagra  lamarckiana  X  Onagra  cruciata  (No.  3.21). 


PLATE  XII. 


7a 


8 


9 


Onagra  lamarckiana  X  Onagra  cruciata  (No.  3.21). 


1,  leaf  from  young  rosette;    2,  leaf  from  median  portion  of  mature  rosette  ;   3,  leaf  from  upper  portio 
of    mature   rosette;    4,  stem-leaf;    5,  bract;  6,  flower   with    petals   removed  (see   6a);    7,  flowe 
with  petals  removed  (see  7a);   8,  petals  of  mininum  size ;    9,  unopened  tlower-bud  ;  10,  capsule 
1  to  4,  one-half  natural   size;     5  to  10,  natural  size. 


MUTANTS   AND    HYBRIDS   OF    THE   OENOTHERAS.  I J 

definitely  stated,  since  no  living  material  of  the  latter  has  been  exam- 
ined. The  only  characters  of  the  hybrid  clearly  derived  from  the 
pistil-parent  are  the  relative  length  of  the  main  axis  and  the  general 
habit  of  branching.  It  is  to  be  said  on  the  other  hand  that  the  cruciata 
characters  to  which  the  general  aspect  of  the  plant  is  largely  due  are 
without  exception  more  or  less  modified.  The  relative  length  of  the 
stamens  and  pistils  was  seen  to  vary  so  that  some  of  the  flowers  were 
capable  of  self-pollination,  while  in  others  the  chance  of  pollination 
without  the  aid  of  external  agencies  was  extremely  small,  so  that  it 
might  be  said  that  in  some  branches  of  the  plant  the  lamarckiana 
character  was  dominant,  while  in  others  the  cruciata  self-fertilizing 
capacity  was  shown.  A  similar  range  of  partial  variability  will  be 
described  in  one  of  the  hybrid  races  of  the  O.  lamarckiana  X  0.  biennis. 
O.  lamarckiana  X  O.  biennis. — The  results  of  the  crosses  made  in 
the  New  York  Botanical  Garden  were  much  more  diversified  than 
those  made  by  De  Vries,  who  obtained  what  he  designates  as  a 
typical  unilateral  hybrid  as  a  result  of  fertilization  of  0.  lamarckiana 
by  O.  biennis  grandiflora.      He  says  (De  Vries,  1903,  p.  31)  : 

The  hybrid  of  Oenothera  biennis  (O.  biennis  grandiflora)  and  O.  lamarckiana 
resembles  the  first  so  strongly  that  they  can  hardly  be  distinguished  from  one 
another.  I  have  made  this  cross  partly  in  1894  and  partly  in  the  summer  of  1899, 
and  in  the  last-named  year  partly  with  0.  lamarckiana  from  my  own  cultures, 
and  partly  from  the  same  species  grown  from  purchased  seeds.  In  all  cases  I 
used  O.  lamarckiana  as  the  mother.  The  stamens  were  taken  from  flowers  of 
plants  in  the  open  (from  unopened  buds),  and  from  plants  of  my  own  cultures 
in  the  last-named  period.  The  bastards  were  of  a  single  type,  and  were  inter- 
changeable with  O.  biennis  (O.  biennis  grandiflora) ,  not  only  in  the  rosettes, 
but  also  in  the  flowers  and  ripe  fruit.  I  had  about  50  flowering  plants  in  1895, 
and  about  70  -f-  60  in  the  two  series  in  1899,  making  altogether  about  180  speci- 
mens in  bloom  in  addition  to  some  with  young  stems  and  rosettes  only  (bien- 
nials). Some  differences  were  seen,  but  they  were  not  so  marked  or  so  important 
that  a  description  could  be  made  of  them. 

I  harvested  some  seeds  in  1895,  which  were  secured  by  artificial  pollination, 
and  the  second  generation  was  grown  from  these  in  the  summer  of  1896.  These 
repeated,  in  the  50  specimens  coming  into  bloom,  only  the  characteristics  of  the 
first-named  parent  (biennis). 

Similarly  the  pollination  of  0.  lamarckiana  by  0.  mnricata  resulted 
in  a  monotypic  unilateral  hybrid  which  approximated  the  pollen- 
parent. 

Four  distinct  types  were  distinguishable  in  the  hybrid  in  New 
York,  and  the  different  forms  could  be  recognized  in  a  very  early 
stage  of  the  seedlings.  All  of  the  individuals  were  easily  seen  to  be 
grouped  around  the  types  mentioned,  and  no  intermediate  or  inter- 
grading  forms  were  found.     The  number  of  individuals  brought  to 


l8  MUTANTS   AND    HYBRIDS   OF    THE    OENOTHERAS. 

maturity  was  comparatively  small,  and  the  possibility  is  not  excluded 
that  a  culture  of  several  hundred  plants  might  include  still  other 
forms.  In  fact,  the  very  differences  between  the  results  of  the  hybrid- 
izations, as  carried  out  in  Amsterdam  and  New  York,  suggest  that  the 
manner  in  which  the  various  qualities  in  the  two  parents  are  grouped 
in  the  progeny  might  be  capable  of  a  wide  range  of  variation.  Many 
indications  lead  to  the  suggestion  that  the  dominancy  and  prevalency, 
latency,  and  recessivity  of  any  character  may  be  more  or  less  influenced 
by  the  conditions  attendant  upon  the  hybridization  ;  the  operative  fac- 
tors might  include  individual  qualities  as  well  as  external  conditions. 
In  addition  to  the  hybrid  individuals  several  specimens  of  the  pistil- 
parent,  lamarckiana,  and  one  of  its  mutants  appeared  in  the  cultures, 
indicating  that  self-fertilization  was  not  entirely  prevented.  This 
might  be  accounted  for  in  two  ways.  Castration  might  not  have  been 
performed  early  enough  to  prevent  the  action  of  pollen  being  scattered 
from  a  bursting  anther  upon  a  mature  stigma  while  the  operation  was 
being  performed.  Then, again,  the  possibility  was  not  wholly  excluded 
that  pollen  from  the  bursting  anthers  which  fell  upon  the  bracts 
inclosed  in  the  parchment  bags  might  have  been  carried  to  the  stigmas 
by  currents  of  air  caused  by  the  compression  or  expansion  of  the 
parchment  bags.  At  any  rate,  the  appearance  of  individuals  of  the 
pistil-parent  type  may  betaken  as  presumptive  evidence  that  such  self- 
pollination  occurred  by  some  method,  although  the  appearance  of 
individuals  of  the  parental  type  in  hybrids  is  well  known. 

(I)  A  type  represented  by  individual  No.  2.1  (PL  XIII,  fig.  1) 
showed  a  rosette  of  deeply  dull-green  leaves,  more  or  less  crinkled 
and  irregular  in  form  and  margin.  In  all  about  twelve  plants  of  this 
type  were  seen,  although  but  five  reached  a  stage  sufficiently  advanced 
to  send  up  a  central  stem.  The  rosettes  were  sparse  and  the  leaves 
thick  and  fleshy,  and  almost  glabrous,  except  that  some  were  minutely 
pubescent  on  the  veins  beneath.  The  leaves  of  the  rosettes  varied 
from  narrowly  linear  in  the  earlier  stages  to  linear-lanceolate  with 
obtuse  apices,  and  to  oblong-spatulate,  broadest  above  the  middle, 
and  acutish  in  some  individuals.  The  laminae  were  revolute  and 
irregularly  denticulate  and  formed  narrow  wings  nearly  to  the  base  of 
the  petioles. 

The  main  axis  of  the  hybrid  individuals  reached  a  height  of  15 
or  20  cm. ,  at  which  stage  in  the  development  elongation  ceased  and  the 
lateral  branches  became  very  active  ;  in  some  instances  no  noticeable 
elongation  of  the  main  axis  occurred.  Branches  of  this  were  more 
rounded  in  outline  and  bore  leaves  of  a  structure  somewhat  more 


PLATE   XIII. 


Fig.  i.     Rosette  five  months  old  of   No.  2.1  of  the  hybrid  Onagra 
lamarckiana  X  Onagra  biennis. 


Fig.  2.     Rosette  five  months  old  of  No.  2.27  of  the  hybrid  Onagra 
lamarckiana  X  Onagra  biennis. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  IO, 

nearly  conforming  to  normal  types  in  a  manner  comparable  to  that  of 
the  parent,  as  noted  above.  These  leaves  were  ovate- denticulate, 
abruptly  acute,  slightly  crinkled,  and  were  minutely  pubescent.  The 
terminal  rosettes  were  dense  and  symmetrical  and  flower-buds  were 
developed,  the  first  of  which  opened  on  August  12.  About  this  time 
some  large  rosettes  were  formed  from  lateral  buds  near  the  bases  of 
the  stems,  which  were  composed  of  oblong-lanceolate  leaves,  slightly 
crinkled  and  denticulate  and  tapering  to  both  ends.  The  entire 
plant  was  tinged  with  red,  and  most  deeply  so  in  the  upper  branches. 
(PL  XVII,  fig.  4O 

The  petals  were  deeply  emarginate,  28  to  30  mm.  long  and  30  to 
35  mm.  wide,  being  broader  than  long  in  all  instances.  The  segments 
of  the  calyx  were  30  mm.  in  length,  being  less  than  half  the  length  of 
the  hypanthium,  which  measured  about  38  mm.  The  ovary  was  10 
mm.  long  and,  with  the  hypanthium,  bore  a  number  of  scattered  hairs. 
Perhaps  the  most  noticeable  feature  of  this  type  was  the  variability  of 
the  relative  length  of  the  stamens  and  pistils.  The  pistils  were  fairly 
constant  in  length,  but  in  some  flowers  the  stamens  were  shorter  and 
therefore  not  adapted  to  self-fertilization,  while  in  others  the  anthers 
were  above  the  stigmas,  thus  insuring  self-pollination.  No  correlated 
structures  were  observed. 

The  capsules  were  about  2  cm.  long,  5  to  6  mm.  wide  below  the 
middle,  oblong,  tapering  from  near  the  base,  obscurely  angled  and 
channeled,  sparingly  pubescent  with  both  long  and  short  scattered 
hairs. 

The  exceptional,  forms  of  leaves  exhibited  by  this  type  were  found 
to  be  accompanied  and  probably  caused  by  the  presence  of  a  fungus, 
which  seemed  to  attack  this  type  only  of  the  hybrid  progeny.  Similar 
effects  in  0.  lamarckiana  have  not  yet  come  under  observation,  but 
young  rosettes  of  0.  biennis,  together  with  mature  plants  coming  into 
bloom,  were  found  growing  wild  in  some  waste  park-land  near  the  New 
York  Botanical  Garden  on  August  21 ,  1904.  The  leaves  of  these  plants 
were  closely  similar  to  those  of  the  pathological  hybrid  individual  in 
general  appearance,  and  furnished  the  curious  parallel  of  showing 
a  partial  return  to  the  normal  form  near  the  upper  ends  of  the  branches. 
Rosettes  of  the  type  described  were  transplanted  to  pots  in  the  experi- 
mental house  and  the  terminal  portions  of  the  leaves  cut  away  in 
accordance  with  garden  practice.  Within  a  few  days  several  leaves 
were  seen  to  show  an  abundance  of  yellowish  spermagonia,  which 
appeared  to  belong  to  Aecidium  peckii  De  Toni,  although  aecidia  were 
not  found. 


20  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

(II)  A  second  type  was  represented  by  individual  No.  2.27,  in 
which  the  leaves  of  the  rosettes  were  finely  pubescent  on  July  1 ;  the 
rosettes  were  widely  spreading  and  the  leaves  finely  pubescent  in 
specimens  examined  on  that  day.  The  laminae  were  lanceolate-oblong 
acute  at  the  apex  and  broadest  above  the  middle,  gradually  narrowing 
to  the  broad  petiole  and  decurrent  upon  it  to  its  base  ;  approximately 
denticulate,  crinkled  between  the  secondary  veins,  more  or  less  spotted 
with  reddish  areas.     (PL  XIII,  fig.  2.) 

Stems  were  sent  up,  which,  upon  examination  on  July  13,  showed 
leaves  of  a  dark  bluish-green  tinge,  the  laminae  becoming  convex 
upwardly  owing  to  the  unecpial  growth  of  the  midrib.  The  stems 
were  dotted  with  the  reddish  bases  of  the  hairs.  The  apices  of  the 
main  stem  and  of  its  branches  formed  close  and  symmetrical  rosettes, 
in  approximation  of  the  structures  shown  by  lamarckiana. 

The  general  habit  of  the  shoot  was  much  like  that  of  biennis,  the 
basal  branches  being  long.  The  central  stem,  however,  was  irregu- 
larly compressed  and  was  of  a  zigzag  form. 

The  flowers  exhibited  the  following  characters:  Corolla-segments 
2.2  cm.  long,  2.5  to  3  cm.  broad  ;  catyx-segments  2.7  cm.  long,  more 
than  half  the  length  of  the  hypanthium;  hypauthium  3.5  cm.  long, 
slightly  pubescent  with  scattered  spreading  hairs  ;  ovary  6  mm.  long, 
also  pubescent  with  scattered  spreading  hairs  ;  anthers  and  stigma  as 
long  as  corolla,  included,  stigma  variously  4  to  6  lobed.  Bracts  nearly 
as  long  as  the  hypanthium. 

Capsules  about  13  mm.  long,  writh  greatest  diameter  6  to  7  mm., 
the  greatest  length  being  about  twice  the  thickness  ;  ovoid-oblong, 
tapering  in  upper  portion  to  obtuse  apex ;  not  angled ;  slightly 
channeled;  sparingly  pubescent  with  appressed  hairs.  (PI.  XV,  fig.  2.) 

(III)  The  third  type  of  the  hybrid  was  represented  by  individual 
No.  2.24,  in  which  the  rosette  was  easily  recognizable  in  the  early 
stages  and  was  dense,  with  the  leaves  lying  flat  on  the  ground  when 
examined  on  July  1.  The  leaves  were  finely  pubescent,  with  broadly 
ovate  laminae,  the  laminae  more  or  less  crinkled,  acutish  or  obtuse  at 
the  apex,  broadest  in  the  middle,  more  or  less  abruptly  narrowed  into 
the  broadly  margined  petiole,  which  is  narrowly  winged  at  the  base. 
These  organs  were  approximately  denticulate  toward  the  apex,  and 
irregularly  dentate  at  the  base,  with  reddish  petioles  and  the  laminae 
sparingly  spotted  with  red.     (PI.  XIV,  fig.  1.) 

The  basal  branches  were  nearly  as  long  as  the  main  axis.  A  por- 
tion of  the  stem  immediately  above  the  base  was  devoid  of  branches. 
The  upper  part  of  the  stem  bore  numerous  erect  branches.  The  stems 
were  deeply  channeled  and  of  a  reddish  color  in  the  lower  portions, 


PLATE   XIV. 


Fig.   i.     Rosette  five  months  old  of    No.  2.24  of   the   hybrid 
Onagra  lamarckiana  X  Onagra  biennis. 


Fig.  2.    Rosette  five  months  old  of  No.  2.32  of  the  hybrid 
Onagra  lamarckiana  X  Onagra  biennis. 


PLATE  XV. 


Fig.  i.  Adult  plant  of  2.1  of  the  hybrid  Onagra  Iamarckiana  :  Onagra 
biennis,  showing  basal  rosette,  pathological  leaves,  normal  leaves  on 
upper  part  of   stem,  buds,  and  flowers. 


Fig.  2.     Onagra  Iamarckiana  X  Onagra  biennis  No.  2.24  at  left, 

No.  2.27  at  right. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  21 

being  distinctly  paler  in  the  terminal  parts,  which  were  of  a  yellowish  - 
green  color.  All  of  the  stems  and  branches  were  terminated  by  tufted 
rosettes.  The  following  characters  were  exhibited  by  the  flowers 
(PI.  XVII,  fig.  5): 

Petals  27  to  31  mm.  long  and  27  to  33  mm.  wide,  deeply  emargi- 
nate  ;  calyx-segments  30  mm.  long,  being  more  than  half  the  length 
of  the  hypanthium,  which  was  48  mm.  in  length,  slender,  and  gla- 
brous, except  for  a  few  scattering  hairs;  ovary  12  mm.  long,  glabrous, 
except  for  a  few  scattered  hairs  ;  stamens  nearly  as  long  as  the 
pistil.  The  capsules  were  29  to  32  mm.  long,  6  to  7  mm.  in  thick- 
ness, being  about  four  times  as  long  as  broad,  distinctly  four-angled, 
and  shallowly  channeled  ;  oblong  and  narrowed  in  the  apical  region  ; 
sparingly  appressed  pubescent.  This  type  was  noted  as  producing 
perfect  seeds  in  apparently  smaller  numbers  than  the  other  types  of  the 
hybrid,  although  some  branches  bore  several  well-filled  capsules. 
(PI.  XV,  fig.  2.) 

(IV)  A  fourth  type  was  represented  by  individual  No.  2.32, 
which  was  not  recognized  in  the  rosette  stage,  although  the  leaves 
are  much  narrower  than  in  0.  biennis,  and  are  not  so  deeply  toothed 
in  the  basal  portion.  The  aspect  of  the  adult  plant  (PI.  XIV,  fig.  2)  is 
very  marked,  however,  and  it  is  easily  recognizable.  The  lateral 
branches  are  numerous  and  nearly  as  long  as  the  main  axis,  with  the 
stems  deeply  channeled.  The  larger  leaves  of  the  rosette  are  narrowly 
oblong-lanceolate  and  yellowish-green,  with  prominent  reddish  mid- 
veins.  The  stem  leaves  are  lanceolate  and  broadest  about  the  middle 
and  deeply  toothed.  The  entire  plant  is  pubescent  and  shows  a  tinge 
of  reddish  color  even  when  young,  which  becomes  much  intensified 
with  age.      (PI.  XIV,  fig.  2.) 

The  bracts  are  oblong-ovate,  the  hypanthium  longer  than  its  seg- 
ments ;  the  petals  are  about  20  mm.  long  and  24  mm.  wide,  with  wedge- 
shaped  bases.  The  stamens,  pistil  and  petals  are  about  of  the  same 
length.  The  green  capsules  are  about  26  to  27  mm.  long  and  6  to  7  mm. 
thick,  oblong,  tapering  from  near  the  base  to  the  narrow  apex,  and 
shining  green,  being  only  sparingly  pubescent.  The  general  outline  of 
the  capsules  is  irregular  ;  in  cross-section  they  appear  distinctly  four- 
angled.     (PI.  XVI,  fig.  3.) 

Seven  individuals  of  this  type  were  brought  to  maturity  and  all 
conformed,  with  only  minor  divergences,  to  the  above  structures. 

The  hybrid  progeny  in  the  cultures  made  in  the  New  York  Botanical 
Garden  and  in  Amsterdam  was  thus  seen  to  include  a  series  of  types 
which   ranged,  in  the  aggregate  of  characters  included,  from  those 


PLATE  XVI. 


/, 


// 


Stem  leaves,  bracts,  petals,  capsules,  and  flowers  of  Onagra  biennis  and  of  two  of 
the  four  hybrid  types  of  Onagra  lamarckiana  X  Onagra  biennis. 

i,  Onagra  biennis ;    2,  No.  2.27;    3,  No.  2.32.     Stem-leaves   one-fourth  natural  size;  remainder  of 

figures  five-eighths  natural  size. 


PLATE  XVII. 


Stem-leaves,  bracts,  petals,  capsules,  and  flowers  of  Onagra  lamarckiana,  and  of  two 
of  the  four  hybrid  types  of  Onagra  lamarckiana  X  Onagra  biennis. 

4,  No.  2.1;  5,    No.  2.24;   6,  Onagra  lamarckiana.    Stem-leaves  one-fourth  natural  size;  remainder 

of  figures  five-eighths  natural  size. 


22  MUTANTS   AND    HYBRIDS    OF   THE    OENOTHERAS. 

representing  pure  strains  of  both  parents  through  goneoclinic  forms 
to  intermediates  in  which  the  parental  characters  were  more  or  less 
equally  apparent. 

Although  the  great  difficulties  attendant  upon  a  valuation  of  the 
characters  occurring  in  hybrids  were  appreciated,  it  was  concluded 
that  such  an  estimation  expressed  in  tabulated  form  would  be  the  best 
method  of  expression  of  the  dominance  of  the  various  characters. 

Hurst  selected  twenty  anatomical  characters  which  were  assigned 
equal  value,  and  included  such  features  as  the  habit  of  growth,  and 
form  and  shape  of  the  leaves  and  other  organs,  and  upon  the  preva- 
lence of  these  characters  the  degree  of  relationship  of  the  hybrid  to 
the  parent  was  estimated.     (Hurst,  1900.) 

Peter  made  a  tabulated  list  of  the  external  characters  of  the 
hybrids  of  the  hawk  weed,  in  which  these  characters  were  classed  as 
unilateral,  goneoclinic,  or  intermediate  with  respect  to  the  corre- 
sponding features  of  the  two  parents.  The  dominance  of  an3r  given 
character  was  calculated  from  its  occurrence  in  the  entire  list  of 
plants  examined.     (Peter,  1884.) 

Mathematical  expressions  of  the  dominance7  of  qualities  are  in 
themselves  misleading  unless  based  upon  actual  physical  measure- 
ments taken  by  statistical  methods  from  a  number  of  individuals  to 
eliminate  errors.  Then,  again,  the  estimation  of  the  development  of 
a  paired  character  presents  one  of  the  greatest  difficulties  encountered 
in  the  study  of  hybrids.  Authors  are  by  no*  means  agreed  as  to  what 
constitutes  absolute  dominance.  Until  within  the  last  few  years  a  char- 
acter was  regarded  as  dominant  by  most  writers  onl}r  when  it  appeared 
in  the  hybrid  as  an  exact  reproduction  of  the  parental  quality.  The 
most  recent  discussion  upon  this  subject  that  has  come  to  notice  is 
that  of  Correns,  who  takes  the  ground  that  a  character  apparently 
representing  the  parental  quality  to  75  per  cent  of  its  full  power  may 
be  considered  as  dominant,  when  occurring  to  the  extent  of  25  to  75 
per  cent  as  intermediate,  and  below  25  per  cent  as  recessive.  (Cor- 
rens, 1903.) 

This  author  calls  attention  to  the  fact  that  fully  dominant  charac- 
ters occur  but  rarely,  and  cites  examples  of  Hyoscyamus  and  Bryonia. 

The  comparatively  small  number  of  individuals  (33)  of  the  hybrid 
between  O.  lamarckiana  and  0.  biennis  which  were  brought  to  ma- 
turity did  not  give  extended  opportunities  for  statistical  work,  and  the 
number  of  characters  taken  into  account  included  many  not  suscep- 
tible of  direct  physical  measurement.  It  was  decided,  therefore,  to 
express  the  descriptions  in  taxonomic  terms  arranged  in  tabulated 
form  to  serve  as  a  graphic  illustration  of  the  general  complexion  of 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


23 


the  types  embraced  by  the  hybrid.  In  this  scheme  it  was  found  most 
convenient  to  apply  the  terminology  generally  used  to  designate  the 
aspect  of  an  individual  to  that  of  the  separate  characters,  and  qualities 
which  were  fully  dominant  and  accurate  representations  of  the  paren- 
tal forms  were  placed  under  the  heading  of  ' '  unilateral ; ' '  those  which 
approximated  the  type  of  one  parent  closely,  but  did  not  represent  it 
sufficiently  to  be  identical  with  it  in  ordinary  descriptive  work,  were 
classed  as  "goneoclinic  "  to  that  type,  while  those  in  which  an  average 
of  the  paired  characters  was  apparent  were  placed  under  ' '  interme- 
diate." It  is  evident  that  the  "intermediate"  of  Correns  would 
embrace  both  the  "  intermediate  "  of  the  above  classification  and  the 
goneoclinic  departure  from  it  on  either  hand.  Goneoclinism  may  well 
be  the  extreme  of  fluctuating  variability  instead  of  a  modification  of 
a  group-quality.  The  scheme  used  below  has  been  found  most  con- 
venient for  this  special  discussion,  but  it  is  not  urged  as  the  best 
method  for  the  general  estimation  of  hybrids. 


Tabulated  analysis  of  the  characters  occurring  in  the  various  types  of  the  hybrid 
Onagra  lamarckiana  X  Onagra  biennis. 

No.  2.1. 


Unilateral. 

Goneoclinic. 

Intermediate. 

Goneoclinic. 

Unilateral. 

To  lamarckiana. 

To  biennis. 

Leaves  dull -green, 
fleshy,  narrow, 
with  irregular  out- 
lines, affected  by 
parasite. 

Lower  leaves  thick, 

Stems    and 
leaves. 

Flowers  and 
fruits. 

Leaves  crinkled. 

Termin  a  1  ro- 
settes symmet- 
rical. 

Upper  leaves 
ovate,  denticu- 
late. 

Capsules  taper- 
ing  to  near 
apex,  short, 
and  thick. 

Relative  length 
of  stamens  and 
pistils  variable. 

waxy,  affected  by 
parasite. 

Calyx  -segments 
shorter  than  hyp- 
anthium. 

The  notable  feature  of  the  structure  of  this  type  consists  of  the  forms  of 
leaves  exhibited  by  the  stem.  The  rosettes  and  leaves  of  the  stem  which  are 
attacked  by  the  fungus  are  almost  exact  counterparts  of  those  of  O.  biennis, 
while  the  upper  portions  of  the  shoot  bear  foliage-organs,  very  similar  to  tihose 
of  O.  lamarckiana.  The  tendency  to  being  attacked  by  the  fungus  seemed  con- 
fined wholly  to  this  type, -which  is  entirely  unlike  the  remainder  of  the  progeny  in 
characters  not  affected  by  the  parasite. 


24 


MUTANTS   AND    HYBRIDS    OF   THE    OENOTHERAS. 


Tabulated  analysis  of  the  characters  occurring  in  the  various  types  oj  the  hybrid 
Onagra  lamarckiana  X  Onagra  biennis — Continued. 

No.  2.32. 


Unilateral.            Goneoclinic. 

Intermediate. 

Goneoclinic. 

Unilateral. 

To  lamarckiana. 

To  biennis. 

Leaves  crinkled. 

Stems  chan- 
neled. 

Terminal  ro- 
settes symmet- 
rical. 

Ovary  sparing- 
ly pubescent. 

Leaves   narrow,  not 

M 

deeply  toothed. 

Leaves  narrow,  deep- 
ly toothed. 

Branches  long  and 
numerous. 

Relative  length  of  hy- 
panthium to  calyx- 
segments  31 : 4 1 . 

Bracts  oblong-ovate; 

petals  wedge-shaped 

at  base. 
Stamens   as  long  as 

pistils ;  pistils  as  long 

as  petals. 

leaves. 

» 

Capsule  oblong, 
tapering  at 
apex. 

Hypanthium  of 
average  length 
of  parents. 

Petals  wider 
than  long. 

Capsule  four- 
angled  and 
tapering  at 
apex. 

fruits. 

Entire  plant  becoming  deeply  tinged  with  red  when  mature. 

No.  2.24. 


Rosettes 

Leaves  crinkled. 

Yo  u  n  g  leaves 

Mature  rosettes    Yo  u  n  g  leaves 

broadly  ovate, 

dense,  spread- 

denticulate. 

acutish  or  ob- 

ing. 

Basal  portion  of 

tuse  at  apex. 

Leaves    broad, 
rounded  at 
apex. 

older  leaves 
irregularly 
denticulate, 
tapering  to 
petiole. 

Stems  and 
leaves. 

Leaves    ovate- 

Basal  branches  as  long 
as  main  axis. 

hanging  down, 

lanceola  te, 

densely  ar- 

denticulate 

ranged. 

throughout. 

Upper  branches 

erect,    spread- 

Flowers and 

ing. 
Bracts    subcor- 

Capsule  nearly 

Petals  interme- 

Hypa n  t  h  i  u  m 

Terminal    rosettes 

fruits. 

date,    oblong- 

glabrous,  ta- 

diate   i  n    size 

thin. 

tufted. 

lanceolate, 

pering  from 

and  in  relation 

Rela  tive  length  of 

acutish,  or 

near    base, 

of  length  and 

hypanthium  and 

acuminate. 

slightly   chan- 
neled. 

breadth. 

*   calyx-segments  as  in 

biennis. 
Relative   length  of 
stamens  and  pistil  as 
in  biennis. 
Capsule     distinctly 
four-angled. 

Among  the  characters  noted  above,  all  may  be  traced  to  the  influence  of  one 
or  other  of  the  parents  directly,  except  that  of  the  excessively  long  and  thin 
hypanthium.  This  organ  sustains  the  proportions  of  some  of  the  large-flowered 
relatives  of  0.  lamarckiana, 


Library 


MUTANTS    AND    HYBRIDS   OF   THE   OENOTHERAS. 


25 


Tabulated  analysis  of  the  characters  occurring  in  the  various  types  of  the  hybrid 
Onagra  lamarckiana  X  Onagra  biennis— Continued. 


Nc 

.  2.27. 

Unilateral. 

Goneoclinic. 

Intermediate. 

Goneoclinic. 

Unilateral. 

To  lamarckiana. 

To  b 

lennis. 

Rosettes 

Leaves  crinkled. 

Mature  rosettes 

Young      leaves 
oblong-lanceo- 

Leaves spotted 
with  red. 

dense,     leaves 

with    long 

late,    tapering 

Leaves    of    ma- 

petioles. 

at  base. 

ture  rosettes, 
lanceolate  -  ob- 
long. 

Stems  and 

Leaves  crinkled. 

Length  of  stem- 
leaves  average 

leaves. 

Terminal    ro- 

ture rosette  not 

settes   dense 

of  parents. 

so  deeply  and 

and   regular, 

regularly  den- 

leaves deeply 

ticulate   as    in 

green. 

biennis. 
Basal  branches 
not  as  long  as 
main  axis. 

Flowers  and 

Basal  portion  of 
petals  rounded. 

Petals   with 

fruits. 

acute,    irregu- 

length  greater 

pistils   of  same 

larly   denticu- 

than width. 

length ;     capa- 

• 

late,    rounded 

Superficial    ex- 

ble of  self-fer- 

or     obscurely 

tension    aver- 

tilization. 

cordate  at  base. 

age  of  parents. 

Capsule  ovoid- • 

Capsule  pubes- 
cent, obscure- 
ly channeled. 

The  stems  were  irregularly  compressed  with  a  zigzag  outline,  in  a  manner 
reminiscent  of  those  of  0.  rubrinervis.  The  upper  leaves  of  the  rosettes  and  of 
the  stems  were  strongly  convexed  upwardly,  due  to  the  unequal  growth  of  the 
laminae  and  midrib.  The  oalyx-segments  were  relatively  shorter  than  in  either  of 
the  parents.    The  entire  shoot  of  the  adult  plant  was  deeply  tinged  with  red. 

It  is  to  be  seen  from  the  foregoing  that  the  hybrid  0.  lamarckiana  X 
0.  biennis  obtained  from  the  crosses  made  in  New  York  includes  four 
distinct  and  separate  forms,  none  of  which  are  identical  with  the  uni- 
lateral monotypic  hybrid  obtained  in  the  same  cross  in  Amsterdam. 
In  the  last-named  form  the  qualities  of  the  pollen-parent  were  fully 
dominant  throughout,  while  in  the  four  types  the  qualities  of  the 
two  parents  exhibit  diversified  mosaics  of  dominancy  and  latency 
of  the  parental  characteristics. 

One  of  the  American  types,  No.  2.1  (PL  XVII,  fig.  4).  was 
characterized  by  a  predisposition  to  the  attacks  of  a  fungal  parasite, 
Aecidium  peckii.  The  portions  of  the  plant  affected  exhibited  structures 
quite  similar  to  those  of  the  pollen-parent  when  affected  by  the  same 
organism.     Organs  not  directly  attacked  by  the  fungus  showed  such 


26  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

distinctive  form  as  to  make  it  certain  that  the  diseased  plants  were  not 
simply  pathological  individuals  of  one  of  the  other  types,  but  that  the 
hybrid  included  a  strain  incapable  of  resisting  the  attacks  of  the  fungus. 
The  entire  crop  of  seeds  obtained  by  the  cross  in  the  previous  year 
were  sown  in  a  single  seed-pan,  and  this  strain  was  seen  to  be  affected 
even  in  the  first  foliage-leaf,  while  all  of  the  others  were  found  to  be 
wholly  immune.  The  whole  pathological  effect  may  be  said  to  be  due 
to  the  dominance  of  qualities  of  biennis.  L,eaves  not  directly  attacked 
by  fungus,  on  the  other  hand,  exhibited  a  predominance  of  qualities 
characteristic  of  O.  lamarckiana.  The  variable  length  of  the  stamens 
and  pistils  may,  however,  most  reasonably  be  ascribed  to  the  patho- 
logical condition. 

A  second  form,  No.  2.32  (PI.  XVI,  fig.  3),  reproduces  the  biennis- 
characters  of  the  bracts,  relative  dimensions  of  the  pistils,  stamens, 
and  petals  quite  exactly,  and  shows  only  slight  departures  from  this 
parent  in  the  habit  of  branching  and  form  and  margins  of  the  leaves. 
The  relative  measurement  of  the  hypanthium  and  of  the  petals  are 
alike  in  the  parents  and  remain  the  same  in  the  hybrid.  Only  one 
character  seems  to  have  been  transmitted  unchanged  from  the  lamarck- 
iana parent,  while  the  stems  are  channeled  something  after  the  manner 
of  this  parent,  and  some  crinkling  of  the  leaves  is  present.  In  this 
instance  the  qualities  of  biennis  predominates  strongly  in  the  hybrid, 
and  the  qualities  inherited  from  the  other  parent  are  of  comparatively 
minor  physiological  importance.  It  is  notable,  however,  that  the 
general  aspect  of  this  plant  is  very  different  from  that  of  biennis, 
although  the  taxonomic  analysis  yields  so  little  actual  anatomical 
divergence.  This  is  partly  due  to  the  unusual  reddish  color  present 
in  the  leaves  and  stems. 

A  third  type,  No.  2.24  (PI.  XVII,  fig.  5),  was  characterized  by 
the  combination  of  parental  qualities  in  such  manner  as  to  constitute 
intermediates.  The  characters  of  the  form,  size,  and  structure  of  the 
stems  and  leaves  made  a  mosaic  of  modifications  from  both  parents,  in 
which  it  would  be  difficult  to  assign  greater  importance  to  one  over 
the  other.  The  hypanthium  exhibited  a  length  greater  than  that  of 
either  parent,  while  the  ovary  was  less  pubescent  than  either.  The 
amount  of  red  color  present  in  the  stems  and  branches  was  much 
greater  than  that  of  either  parent  and  is  only  duplicated  among  some 
of  the  related  species  of  the  genus. 

The  form  and  structure  of  the  bracts  and  the  crinkling  of  the 
leaves  were  transmitted  unchanged  to  the  individual ;  the  size  and 
form  of  the  petals  were  intermediate,  and  the  relative  length  of  the 
calyx-segments  and  hypanthium  of  biennis  were  found.     It  was  notable 


PLATE  XVUI. 


Onagra  gigas. 

leaf  from  middle  of  main  stem  ;  2,  leaf  from  main  stem  ;  3,  bract  from  one  of  the  lowermost  flowers  ; 
4,  flower  with  petals  removed  ;  5,  petal ;  6,  leaf  from  lower  part  of  rosette  five  months  old  ;  7,  leaf 
from  upper  part  of  rosette  five  months  old  ;  8,  capsules.  1, 2,  3,  4,  5,  and  8,  five-eighths  natural  size; 
6  and  7.  one-fourth  natural  size. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  27 

that  the  spread  of  foliar  surfaces  and  the  density  of  arrangement  of 
the  leaves  was  similar  to  lamarckiana,  while  the  form,  incisions  in  the 
margin,  and  arrangement  at  apices  of  branches  were  similar  to  biennis. 
In  the  same  manner  the  capsule  was  nearly  glabrous,  but  was  found 
to  be  distinctly  four-angled. 

A  fourth  type,  No.  2. 2  7,  bore  flowers  not  easily  distinguishable  from 
the  pollen-parent,  being  capable  of  self-fertilization,  but  with  the  parts 
of  the  flower  of  greater  size.  From  the  other  parent  the  unequal  growth 
of  the  leaves,  which  results  in  the  crinkling  of  the  laminae  is  shown 
with  a  modification  which  causes  convexities  and  concavities. 

The  symmetrical  terminal  rosettes  are  also  a  lamarckiana  charac- 
ter of  the  entire  laminae.  An  analysis  of  the  remaining  characters  show 
that  nearly  all  are  combinations  of  parental  qualities.  Perhaps  the 
most  remarkable  feature  of  this  type  is  the  appearance  of  qualities 
usually  exhibited  only  by  species  allied  to  the  parents  and  not  by  the 
parents  directly.  Among  these  may  be  mentioned  the  zigzag  forma- 
tion of  the  stem  and  the  red  coloration  of  the  shoot. 

In  view  of  the  above  results  it  is  evident  that  a  repetition  of 
the  crosses  between  the  mutant  derivatives  of  0.  lamarckiana  and  0. 
biennis  would  yield  much  of  interest.  De  Vries  has  repeatedly  called 
attention  to  the  fact  that  the  prevalency  of  the  parental  types  in  crosses 
of  mutants  with  each  other  and  with  the  parental  form  may  be  altered 
by  nutritive  conditions,  and  it  may  well  be  supposed  that  a  similar 
state  of  affairs  may  be  found  to  exist  in  the  hybrid  described  above. 

It  will  be  of  interest  to  trace  the  dominancy  of  the  separate  charac- 
ters of  the  two  parents  throughout  the  hybrid  considered  as  a  whole. 
Of  these  the  one  that  may  be  seen  earliest  in  the  development  of  the 
plantlets  is  the  density  of  the  rosettes  due  to  the  rapidity  with  which 
the  leaves  on  the  shortened  internodes  of  the  young  stems  appear,  and 
their  duration.  Every  individual  in  the  hybrid,  without  exception, 
showed  a  heavy  rosette  composed  of  about  12  to  20  leaves,  after  the 
manner  of  lamarckiana.  Plantlets  of  biennis  of  a  similar  age  never 
bore  more  than  half  that  number.  The  character  in  question  depends 
upon  the  activity  of  the  internode ;  the  dominant  character  entails  a 
more  rapid  succession  of  development  in  these  members,  as  no  differ- 
ence could  be  detected  in  the  duration  of  the  individual  leaves. 
While  the  character  itself  would  be  classed  as  meristic  in  its  nature, 
yet  it  is  really  seen  to  rest  upon  a  real  and  constant  physiological 
quality.  In  addition  to  the  rate  of  growth,  it  is  not  improbable  that 
the  greater  density  of  the  dominant  rosette  may  be  due  in  part  to  the 
development  of  a  greater  number  of  internodes  before  the  elongated 
flowering  shoot  is  sent  up. 


28  MUTANTS  AND    HYBRIDS   OF   THE   OENOTHERAS. 

The  leaves  of  all  rosettes  of  the  hybrid  showed  laminae  variously- 
crinkled,  caused  by  the  unequal  growth  of  the  mesophjdlary  and  fibro- 
vascular  tracts  of  the  laminae,  a  character  which  is  well  marked  and 
constant  in  0.  lamarckiana,  but  which  was  not  seen  in  0.  biennis  in 
any  of  the  cultures,  although  it  has  been  seen  in  a  few  wild  specimens 
which  were  growing  luxuriantly.  Furthermore,  the  crinkling  of  the 
leaves  was  exhibited  in  the  stem-leaves  of  the  entire  hybrid.  In  one 
type,  that  illustrated  by  2.27  and  consisting  of  two  individuals,  a 
further  lack  of  correlation  in  the  growth  of  the  tissues  of  the  leaf  was 
exhibited,  which  consisted  in  an  excess  growth  of  the  midrib  over 
that  of  the  wings  of  the  laminae,  giving  it  an  upward  convexity  which 
might  easily  be  converted  into  the  reverse  form.  This  was  present  in 
both  the  rosette  and  stem-leaves. 

The  forms  of  leaves  were  so  diversely  intermediate  that  it  is  not  pos- 
sible to  point  to  any  important  dominancies  in  this  respect,  except  such 
as  are  found  in  the  types  of  terminal  rosettes  exhibited  by  stems  and 
branches.  One,  a  regular,  flattened,  and  symmetrical  rosette,  charac- 
teristic of  lamarckiana,  was  dominant  in  all  individuals  except  those 
of  2.24,  which  bore  tufted  rosettes  in  the  five  individuals  included 
with  it. 

The  branching  habit  of  0.  biennis,  by  which  secondary  members 
were  borne  on  all  parts  of  the  main  axis,  decreasing  in  length  upwardly, 
showed  exactly  the  complementary  prevalency,  being  present  in  all 
individuals  with  terminal  rosettes  of  the  pattern  of  0.  lamarckiana. 
Type  No.  2.24,  which  bore  bie?inis  rosettes,  gave  off  large  basal 
branches,  and  the  upper  part  of  the  main  axis  was  more  densely 
branched  than  in  0.  lamarckiana,  so  that  the  habit  of  the  pistil-parent 
in  this  particular  was  not  exhibited  in  pure  form  by  any  member  of 
the  hybrid. 

Stems  of  rounded  cross-section  were  found  to  be  more  prevalent 
than  those  with  deep  channeling,  the  latter  occurring  on  only  five  indi- 
viduals of  the  hybrid. 

The  capacity  for  self-fertilization  as  indicated  by  the  relative 
length  of  the  stamens  and  pistil  was  dominant  in  all  types,  except  that 
of  2.1,  or  in  about  29  out  of  the  33  individuals  examined.  A  sharp 
separation  with  regard  to  this  character  may  be  detected  in  securing 
pure  fertilizations.  In  order  to  obtain  capsules  with  pure  seeds  it  is 
but  necessary  to  inclose  the  inflorescences  of  0.  biennis  in  the  parch- 
ment bags  and  the  pollen  will  fall  on  the  stigmatic  surfaces  without 
the  intervention  of  any  agency  whatever  except  gravity.  On  the  other 
hand,  0.  lamarckiana  rarely  sets  seeds  unless  pollen  is  transferred  to 
the  stigmas  by  insects  or  by  hand,  although  in  the  open  air  the  same 
purpose  is  sometimes  accomplished  by  the  wind. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  20, 

The  calyx-segments  are  relatively  much  shorter  than  the  hypan- 
thium  in  all  individuals  of  the  hybrid  showing  a  dominance  of  a  char- 
acter of  O.  biennis,  although  the  actual  length  of  the  latter  is  greater 
in  some  individuals  than  in  either  parent.  The  other  features  of  the 
flowers  were  variously  intermediate.  The  elongated  capsule  was  pres- 
ent in  all  of  the  individuals  of  the  hybrid,  except  in  the  two  included 
in  the  type  of  No.  2.27. 

OCCURRENCE  OF  MUTANTS. 

Among  the  progeny  arising  from  the  cross  between  0.  lamarckiana 
and  0.  biennis  were  two  individuals  which,  as  early  as  July  1,  were 
seen  to  be  separable  by  the  variously  erect  leaves  with  long  petioles 
in  the  rosettes.  The  rosettes  were  sparse,  and  the  leaves  were  oblong- 
lanceolate,  obtuse  at  the  apex,  broadest  about  the  middle,  and  more 
or  less  abruptly  narrowing  to  the  petiole,  upon  which  the  narrow 
wings  of  the  laminae  extended  nearly  to  the  base.  The  basal  portions 
of  the  leaves  were  deeply  and  irregularly  denticulate.  The  members 
of  the  rosette  were  minutely  pubescent.  On  July  13  these  plants  had 
sent  up  shoots  which  soon  bore  the  characteristic  leaves,  bracts,  and 
flowers  of  0.  rubrinervis,  a  mutant  which  was  originally  observed  by 
De  Vries  in  1887. 

The  occurrence  of  mutants  in  hybrids  in  which  one  of  the  parents 
appears  as  a  pure  strain  has  long  been  known  and  has  been  described 
at  length  by  Professor  De  Vries  as  occurring  at  numerous  times  in 
his  cultures.  He  found  that  about  1  per  cent  of  the  hybrid  progeny 
of  0.  lamarckiana  X  0.  nanella  was  composed  of  mutants,  and  that 
about  2  per  cent  of  the  hybrid  progeny  between  various  older  species 
were  mutants  in  a  series  of  tests  made  in  1896-1900.  (De  Vries,  1903, 
pp.  425,  426.) 

0.  rubrinervis  was  observed  by  De  Vries  to  arise  in  the  hybrid 
progeny  of  0.  lamarckiana  X  nanella,  0.  lata  X  nanella,  0.  lata  X 
lamarckiana,  0.  lataX  brevistylis,  0.  nanella  X  brevistylis,  0.  scintillans 
X  nanella,  and  0.  lamarckiana  X  scintillans,  to  which  must  be  added 
the  experience  related  above,  by  which  this  species  was  also  found  in 
the  descendants  of  0.  lamarckiana  X  biennis. 

The  facts  recorded  by  De  Vries  indicate  that  the  mutability  of  the 
various  forms  of  the  evening-primrose  is  not  modified  by  crossing  in 
any  manner.  It  is  a  matter  of  interest  in  this  connection  that  he  has 
also  established  the  conclusion  that  the  number  and  amplitude  of 
fluctuating  variations  exhibited  by  parental  forms  are  not  increased 
or  materially  modified  in  the  hybrids. 


30  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

The  designation  of  an  individual  from  a  hybrid  progeny  as  a 
mutant  is  unsafe,  unless,  as  in  the  evening- primroses,  the  characters 
of  the  mutants  have  been  established  by  previous  observations.  It  is 
quite  possible  that  mutants  may  have  appeared  in  hybrids  at  various 
times,  thus  giving  basis  for  the  assumption  that  new  qualities  were 
seen  to  appear  as  a  result  of  the  hybridization. 

A  second  occurrence  of  O.  rubrinervis  as  a  possible  mutant  was 
noted  in  a  lot  of  plantlets  grown  from  seeds  obtained  from  the  botan- 
ical garden  at  Upsala  early  in  1904.  The  seeds  were  sown  in  germi- 
nating pans  on  March  28,  1904,  and  four  individuals  were  transplanted 
to  the  experimental  grounds  on  May  28  and  began  to  send  up  shoots 
early  in  July.  Of  these,  two  were  undoubted  types  of  0.  rubrinervis , 
corresponding  to  this  form  in  all  particulars. 

In  reply  to  the  inquiry  as  to  the  derivation  of  the  seed  from  which 
the  above  plants  were  grown,  Prof.  F.  R.  Kj  ell  man,  director  of  the 
botanical  garden  at  Upsala,  replied  as  follows  under  date  of  August 
8,  1904: 

The  seeds  of  Oenothera  lamarckiana,  which  you  received  from  this  botanical 
garden,  were  gathered  from  plants  grown  in  a  cool  house  from  seeds  obtained 
from  Professor  De  Vries.  Some  Oenotheras  of  other  species  were  growing  near 
these  plants,  upon  which  account  the  possibility  of  hybridization  was  not  ex- 
cluded. Pure  seeds  of  the  new  species  of  Oenothera  may,  in  my  opinion,  only 
be  obtained  from  Professor  De  Vries. 

In  view  of  theabove  record,  therefore,  it  may  only  be  said  that  the 
specimens  of  O.  rubrinervis  in  this  culture  owe  their  origin  either  to 
an  actual  mutation,  or  to  the  pollination  of  0.  lamarckiana  by  0. 
rubrinervis .  Professor  Kjellman  did  not  state  whether  or  not  any  of 
the  new  species  were  included  in  the  lot  growing  near  0.  lamarckiana, 
although  the  negative  presumption  seems  warranted. 

Still  a  third  occurrence  of  the  same  species  is  to  be  noted,  for 
which  all  explanation  is  lacking  at  the  present  time.  A  package  of 
seeds  under  the  label  of  "  Statice  Japonica  "  were  received  from  the 
botanical  garden  at  Tokyo,  in  1903.  After  germination,  four  of  the 
seedlings  were  transplanted  to  small  pots  in  accordance  with  the  usual 
custom  with  new  accessions  to  the  New  York  Botanical  Garden. 
Attention  was  not  called  to  the  peculiar  appearance  of  these  plants 
until  early  in  May,  when  they  formed  rosettes  2  dm.  in  diameter,  and 
were  unmistakably  0.  rubrinervis.  I  was  not  able  to  trace  the  history 
of  the  seed-package  and  learn  whether  all  of  the  seeds  were  of  the  same 
kind  or  not.  If  by  mistake  a  package  of  seeds  of  Onagra  had  been 
sown  under  the  above  label,  the  rubrinervis  which  was  with  it  would 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  3 1 

have  germinated  first,  as  the  seeds  are  very  easily  awakened  from  the 
dormant  condition,  and  a  half  dozen  of  these  would  have  been  trans- 
planted to  small  pots  by  the  gardener  and  the  remainder  would  have 
been  destroyed  in  accordance  with  the  usual  custom.  A  still  further 
possibility  lies  in  the  fact  that  ordinary  seeds  are  sown  in  mixtures  of 
potting  soil  that  has  not  been  sterilized,  and  might  have  contained 
some  seeds  of  this  species  from  the  cultures  made  in  the  New  York 
Botanical  Garden  for  the  previous  year. 

The  chief  purpose  of  the  earlier  studies  of  the  senior  author  of  the 
present  paper  was  to  make  comparative  studies  of  the  parent-form  with 
its  mutant  derivatives,  and  also  to  test  the  stability  of  all  of  the  types 
concerned  when  cultivated  under  climatic  conditions  widely  different 
from  those  under  which  the  mutants  arose.  Previously  to  the  cul- 
tures of  1904  less  than  a  dozen  of  the  various  forms  were  brought  to 
maturity,  and  no  attention  was  given  to  the  possible  occurrence  of 
mutants  among  the  seedlings,  although  many  might  have  been  present. 
Thus  DeVries found  600  mutants  in  50,000  seedlings  from  lamarckiana , 
although  he  has  pointed  out  that  it  would  be  possible  to  have  exten- 
sive plantations  of  seedlings  which  included  no  divergent  forms. 
Still  another  factor  in  the  matter  consisted  in  the  inexperience  of  the 
experimenter.  The  discovery  of  the  mutants  in  the  seedling  stage 
when  only  two  or  three  small  leaves  are  present  is  difficult  for  the  first 
time,  although  after  becoming  accustomed  to  the  typical  forms  and 
learning  the  aspect  of  the  things  to  be  looked  for  it  is  compara- 
tively easy  to  recognize  the  better-known  mutant  types.  Even  then 
the  mutants  previously  seen  are  much  more  readily  distinguished  than 
those  known  only  by  descriptions.  This  matter  of  practical  observa- 
tion depends  greatly  upon  the  plain  mechanical  fact  that  the  selection 
of  the  various  forms  is  generally  done  in  the  seed-pans  in  which  ger- 
mination occurred  in  order  to  save  the  labor  necessary  in  transplanting 
them  to  small  pots. 

After  the  major  ends  of  the  cultures  had  been  reached  in  the 
summer  of  1904,  and  the  newly -grown  crops  of  seed  were  nearly 
mature,  the  chances  of  losing  any  of  the  forms  under  cultivation  by 
accident  was  reduced  to  a  minimum,  and  all  of  the  seeds  remaining  on 
hand  were  sown  in  pans  of  sterilized  soil  in  order  to  make  separate 
observations  upon  the  occurrence  of  mutants.  Several  thousands  of 
seeds  of  0.  lamarckiana  of  the  crop  of  1901  from  the  botanical  garden 
of  Amsterdam,  and  of  the  same  species  of  the  crop  of  1903  from  the  New 
York  Botanical  Garden,  were  germinated  in  the  above  manner.  In 
addition,  a  few  hundred  seeds  of  0.  gigas  of  the  crop  of  1903  from  the 
botanical  garden  of  Amsterdam  were  sown 


32  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

The  seedlings  of  the  last-named  species  show  a  wide  divergence 
in  the  juvenile  leaves,  which  is  partially  continued  even  in  the  foliar 
organs  of  the  mature  plant,  although  it  is  not  believed  that  these 
divergences  may  be  grouped  in  separate  strains  of  the  species.  Con- 
sequently several  selections  were  made  from  the  cultures  which,  how- 
ever, were  soon  found  to  be  well  within  the  limits  of  the  type. 

The  results  obtained  from  0.  lamarckiana  were  of  much  greater 
interest.  Mutants  were  found  in  the  seedlings  grown  directly  from 
the  seeds  from  the  garden  at  Amsterdam,  and  also  from  those  of  1904 
from  the  New  York  Botanical  Garden.  As  early  as  October  1,  1904, 
O.  albida,  0.  elliptica,  and  0.  scintillans  were  recognizable  in  the  plant- 
lets  grown  from  seeds  produced  in  New  York  and  Amsterdam. 
Later,  gigas,  nanella,  oblonga,  and  subovata  were  found.  In  addition 
to  these  seven  known  mutants  which  had  been  seen  to  originate 
previously  in  Amsterdam,  seven  other  forms  could  be  distinguished 
which  could  not  be  identified  with  any  forms  heretofore  observed  by 
Professor  De  Vries  or  the  authors.  It  is  therefore  justifiable  to  say 
that  so  far  as  present  information  goes  the  range  of  mutability  of  the 
parent-species  has  been  extended  under  the  conditions  under  which  it 
has  been  cultivated  in  America.  A  comparative  examination  of  the 
cultures  in  the  two  localities  brings  out  the  fact  that  the  plants  grown 
in  New  York  were  much  more  vigorous  and  active  than  those  in 
Amsterdam,  and  the  suggestion  lies  close  at  hand  that  whatever  the 
causes  may  be  that  induce  changes  in  the  qualities  of  a  species,  the 
actual  environment  in  which  such  mutative  alterations  ensue  is  one 
that  has  a  majority  of  the  factors  favorable  to  vegetative  development 
as  well  as  to  plentiful  seed-production.  The  limited  number  of  facts 
brought  to  light  by  the  mutation  cultures  certainly  support  the  sug- 
gestion in  question,  which,  it  is  to  be  noted,  is  in  direct  opposition  to 
the  conclusion  of  Darwin  that  new  types  arise  most  plentifully  in 
response  to  adverse  circumstances. 

In  conjunction  with  the  foregoing  it  is  to  be  recalled  that  seeds  of 
0.  lamarckiana  obtained  from  Vilmorin-Andrieux  et  Cie.,  in  France, 
by  De  Vries,  produced  some  0.  nanella  when  sown  in  the  botanical 
garden  at  Amsterdam  in  1899.     (De  Vries,  1903,  p.  459.) 

It  is  to  be  seen,  therefore,  that  0.  lamarckiana.  is  still  in  a  mutable 
condition  in  various  portions  of  its  widely  extended  range.  The 
results  of  the  more  recent  cultures  made  in  the  botanical  garden  at 
Amsterdam  leads,  however,  to  the  conclusion  that  0.  lamarckiana 'has 
lost  the  capacity  for  producing  0.  lata,  laevifolia,  and  brevistylis.  De 
Vries  also  found  that  the  capacity  for  mutability  inherited  by  rubri- 


Plate  xix. 


Fig.  i.     Onagra  lamarckiana  and  Onagra  nanella  in  bloom. 

Photographed  at  6  a.  m.,  August  g'  1904. 


$m. 


% 


Fig.  2.     Onagra  lamarckiana  X  Onagra  biennis. 
No.  2.32  at  left  and  right  in  foreground;  No.  2.24  in  center. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  33 

nervis,  by  which  it  was  able  to  give  rise  to  nanella,  no  longer  exists. 
The  loss  of  mutability  has  been  noted  to  be  accompanied  by  an  acqui- 
sition of  the  Mendelian  procedure  in  the  hybridization  of  these  two 
forms.     (De  Vries,  1903,  pp.  458,  460.) 

The  discovery  of  single  plants  presumably  derived  from  an  ances- 
tral mutation,  or  of  a  few  plants  as  mutants  from  a  parent,  suggest 
that  in  some  instances  the  period  of  mutability  of  a  species  may 
include  only  a  single  season,  and  these  brief  periods  may  recur  at 
intervals  concerning  which  information  is  totally  lacking.  In  the  case 
of  Oenotheras,  however,  the  first  mutants  in  bloom  were  found  in  1887, 
which  shows  that  the  parents  from  which  they  were  derived  perfected 
their  seeds  in  1885.  The  recurrence  of  various  mutants  has  been  noted 
in  every  succeedingyear,  including  1904,  and  it  is  to  be  seen,  therefore, 
that  this  species  has  been  in  a  mutable  condition  for  twenty  years. 
How  much  earlier  mutants  have  been  formed  than  the  date  given 
above  cannot  be  surmised.  The  continuance  of  the  capacity  for  muta- 
bility is  open  to  actual  observation,  however,  and  it  may  be  possible 
within  fthe  next  few  years  for  the  botanist  to  actually  witness  the 
closing  of  the  mutative  period  in  this  plant  which  has  furnished 
material  so  rich  in  practical  and  theoretical  results.  The  procedure  of 
O.  lamarckiana  is  supposed  by  De  Vries  to  be  similar  to  that  which 
has  been  followed  by  Draba  and  Viola  in  the  productions  of  the 
swarms  of  species  now  recognized.     (De  Vries,  1905.) 

During  the  cultures  of  1902- 1903  O.  lamarckiana,  O.  nanella,  and 
O.  rubrinervis  were  grown  as  biennials  for  purposes  of  comparison 
with  the  behavior  of  other  species.  During  1904,  however,  seeds  were 
sown  in  the  propagating  houses  about  the  first  of  the  year  and  the 
plantlets,  after  being  properly  transferred  from  smaller  to  larger  pots, 
were  placed  in  the  soil  in  the  experimental  grounds  in  the  latter  part 
of  May.  No  marked  difference  between  the  two  series  could  be 
detected.  It  was  noted  that  0.  gigas,  however,  has  more  thoroughly 
established  itself  in  the  biennial  habit  and  that  not  half  of  the  plants 
grown  as  annuals  actually  produced  flowers  or  seeds  in  1904. 

The  estimation  of  the  general  hardiness  or  fitness  of  the  parental 
form  and  of  the  mutants,  with  a  view  to  the  determination  of  their  rel- 
ative value  if  thrown  into  a  competitive  struggle  for  existence,  is  not 
to  be  too  lightly  made.  O.  lamarckiana  has  not  spread  over  any  part 
of  North  America  having  the  climate  of  New  York,  and  its  cultivation 
in  this  locality  must  bring  into  contact  many  factors  inoperative  in  its 
natural  habitat.  Tests  made  under  such  conditions  must  be  accepted 
most  guardedly.  A  general  description  of  some  of  the  more  striking 
characteristics  of  the  various  forms  will  be  of  some  value,  however. 


34 


MUTANTS   AND    HYBRIDS    OF    THE   OENOTHERAS. 


The  rosettes  of  0.  lamarckiana  and  0.  rubrinervis  which  failed  to 
send  up  flowering  shoots  in  1903  endured  the  following  winter,  which 
was  of  maximum  severity,  and  began  growth  in  a  normal  manner  in 
the  spring  of  1904,  but  were  uprooted  to  make  room  for  a  new  series  of 
experiments. 

No  actual  difference  has  been  found  in  the  power  of  producing 
pollen  among  the  parent-form,  the  mutants  grown  in  the  New  York 
Botanical  Garden,  and  the  other  American  species.  All  produce  an 
abundant  crop  of  pollen,  and  show  many  faulty  grains.  0.  rubrinervis 
was  found  to  produce  a  greater  number  of  capsules,  and  the  seeds  ger- 
minated more  readily  than  those  of  the  parent-form,  the  plants  reaching 
maturity  earlier  than  0.  lamarckiana.  O.  gigas,  on  the  other  hand, 
grows  more  slowly  than  the  parent-form,  as  stated  above,  although  it 


Fig.  2.    Seedlings  of  Onagra  gigas,  about  Ave  weeks  old,  showing  variations 

in  forms  of  leaves. 


produces  seeds  abundantly,  which  show  a  high  percentage  of  germina- 
tion. Both  species  are  supposed  by  De  Vries  to  be  quite  equal  to  the 
parental  type  in  vigor,  or  perhaps  to  excel  it.  The  latter  suggestion 
is  supported  by  the  marked  reproductive  capacity  of  these  forms  in 
hybridizations  When  crossed  with  the  parental  form  or  with  other 
mutants,  the  dominance  of  the  characters  of  0.  gigas  and  O.  rubri- 
nervis is  especially  marked,  most  so  in  the  case  of  0.  gigas. 

In  continuation  of  the  work  carried  on  in  previous  cultures  obser- 
vations of  0.  gigas  were  made  for  the  purpose  of  placing  on  record  an 
exact  description  of  its  characteristics  as  grown  in  America.  The 
formal  descriptions  of  the  parental  type  andO.  rubrinervis  and  O.nanella 
have  already  proved  useful  in  the  various  phases  of  the  present  investi- 
gation.    (MacDougal,  1903.) 


PLATE    XX. 


Fig.  i.   Onagra  gigas  in  bloom. 

Photographed  at  7  a.  m.,  August  9,  1904. 


Fig.  2.    Rosettes  ot  Onagra  gigas  six  months  old,  show  ing  diverse  forms  ol  lea\  es. 


PLATE    XXI. 


Onagra  rubrinervis. 

Photographed  at  6.30  a.  m.,  August  9,  1904- 


PLATE    XXII. 


A  series  of  leaves  taken  from  near  the  middle  of  the  basal  branches  ol  On 
lamarckiana  and  Onagra   rubrinervis,  illustrating  the  nearest  approach  to 
identity  in  leaf-form.    The  two  lower  rows  are  Onagra  rubrinervis  ;  the  two 
upper  Onagra  lamarckiana. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  35 

ONAGRA  (OENOTHERA)  GlGAS. 

Seedling  about  two  months  old. — Leaves  finely  but  rather  copiously 
pubescent ;  blades  various  ;  those  of  the  earlier  leaves  narrowly  or 
broadly  oblong,  those  of  the  later  leaves  broadly  oval,  suborbicular, 
or  ovate-orbicular,  mainly  3  to  4  cm.  wide,  abruptly  narrowed  at  the 
base,  or  truncate,  longer  than  the  petiole. 

Seedling  five  months  old. — Rosettes  rather  dense;  leaves  copiously 
fine-pubescent;  blades  broadly  oblong,  oval,  or  ovate,  varying  to 
obovate,  the  larger  ones  2.5  cm.  wide,  distantly  denticulate,  obtuse  or 
nearly  acutish  at  apex,  markedly  longer  than  petiole.    (PI.  XX,  fig.  2.) 

Mature  rosette. — Leaves  ample,  finely  pubescent  all  over,  the 
larger  ones  about  28  cm.  long,  9  to  10  cm.  wide  ;  blades  ovate  and 
prominently  glandular-denticulate,  or  with  an  ovate  terminal  lobe  and 
several  large  basal  teeth,  or  tooth-like  lobes,  with  petioles  very  stout. 

Adult  plant. — Plant  very  stout  and  luxuriant.  Stem  channeled, 
branched  near  the  base,  and  mainly  below  the  middle,  the  branches 
assurgent  or  ascending,  like  the  main  stem  hirsute,  the  hairs  com- 
monly widely  spreading  ;  leaves  finely  pubescent,  1  to  2  dm.  long,  on 
the  lower  part  of  the  stem,  numerous  ;  blades  shallowly  and  rather 
remotely  toothed,  those  of  the  lower  cauline  leaves  oblong-spatulate  to 
oblong,  acute  at  the  apex,  each  narrowed  into  a  semi-terete,  margined 
petiole,  those  of  the  upper  leaves  broadly  oblong  to  oblong-ovate,  acute 
or  abruptly  short-acuminate,  sessile  or  nearly  so ;  bracts  ovate-lanceo- 
late, cordate  or  subcordate  at  the  base;  conic  portion  of  the  bud  about 
3.5  cm.  long,  finely  pubescent,  with  short,  spreading  hairs,  the  free  tips 
of  the  sepals  6  to  7  mm.  long  ;  hypanthium  4  to  4.5  cm.  long,  about 

7  mm.  wide  at  the  mouth,  slightly  ribbed  ;  sepals  4  to  4.5  cm.  long, 
about  as  long  as  the  tubular  portion  of  the  hypanthium,  the  free  tips 

8  to  9  mm.  long;  petals  firm,  4.5  to  5  cm.  long,  truncate  or  slightly 
emarginate  at  the  apex;  filaments  18  to  20  mm.  long  ;  anthers  15  to 
16  mm.  long;  pistil  longer  than  the  stamen ;  stigma  6  to  7  mm.  long ; 
capsule  about  2  mm.  long,  7  to  8  mm.  in  diameter  at  thickest  point, 
finely  pubescent  all  over,  scarcely  narrowed  at  apex.     (PL  XVIII.) 


36  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

STATISTICAL  COMPARISONS   OF  ONAGRA  (OENOTHERA)  LAMARCK- 
IANA  WITH  TWO  OF  ITS  MUTANTS .* 

So  general  is  the  experience  in  garden  practice  that  a  variety 
which  has  been  improved  by  selection  rapidly  loses  its  improved 
character  upon  the  cessation  of  the  selective  process  that  the  sta- 
bility of  any  modification  which  is  discovered  either  in  nature  or 
under  cultivation  demands  the  fullest  possible  proof.  The  mutation - 
theory  is  so  diametrically  opposed  to  Galton's  law  of  ancestral 
heredity  that  it  needs  especial  investigation  from  the  same  standpoint 
and  by  the  same  methods  by  which  this  law  was  established.  Accord- 
ing to  Galton's  law  the  offspring  shows  a  certain  definite  degree  of 
inheritance  from  each  generation  of  its  ancestors,  one-half  from  its 
parents,  one-quarter  from  its  grandparents,  one-eighth  from  its  great - 
grandparents,  and  so  on.  (Gal ton,  1889.)  As  a  consequence  of  this 
law  the  children  of  extreme  parents  are  on  the  average  less  extreme 
than  their  parents,  because  their  preparental  ancestry  is  on  the  average 
more  mediocre.  The  departure  of  the  offspring  from  the  mean  con- 
dition of  the  race  to  which  it  belongs  toward  the  extreme  condition  of 
its  parents  has  been  designated  ' '  regression. ' '  One  of  the  most  serious 
criticisms  which  has  been  made  upon  De  Vries's  conclusions  has  been 
that  of  Weldon ,  who  points  out  that  no  satisfactory  evidence  has  been 
presented  to  prove  the  completeness  of  regression,  in  the  Galtonian 
sense,  in  the  Onagra  mutants.  For,  unless  such  regression  is  com- 
plete, these  mutants  could  not  maintain  themselves  distinct  from  the 
parental  type  except  through  the  agency  of  man  in  guarding  pollina- 
tion and  in  selection,  a  fact  which  wtmld  deprive  them  of  all  signifi- 
cance in  the  explanation  of  evolution.    (Weldon,  1902.) 

To  test  quantitatively  the  continuity  or  discontinuity  of  a  few  of 
the  differential  characters  of  the  Onagra  mutants,  and  to  begin  the 
work  which,  when  continued  for  several  years,  will  forever  set  at  rest 
the  question  of  the  completeness  of  Galtonian  regression,  the  investi- 
gation the  results  of  which  are  reported  in  this  section  were  undertaken. 
The  number  of  specimens  available  for  study  was  not  sufficient  for  the 
most  satisfactory  statistical  work,  but  the  results  offer  a  number  of 
suggestive  lines  for  future  investigation. 

As  all  the  characters  chosen  for  this  investigation  are  notably 
affected  by  the  physical  conditions  to  which  the  plants  are  subjected, 
it  should  be  pointed  out  that  all  these  specimens  were  grown  near 
each  other  in  an  experimental  garden  which  presents  nearly  uniform 
conditions  throughout,  and  that  they  were   planted  at  the  uniform 


*Prepared  by  G.  H.  Shull. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  ^J 


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38  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

distance  from  each  other  of  one  meter,  thus  allowing  each  specimen 
sufficient  space  to  express  its  characteristic  physiological  nature 
unmodified  by  complex  interrelations  with  other  plants. 

The  stature  of  Onagra  nanella. — The  character  which  most  strik- 
ingly differentiates  0.  nanella  from  its  parent-form,  O.  lamarck- 
iana,  is  that  from  which  it  has  so  appropriately  received  its  name. 
The  great  difference  in  height  between  these  two  species  may  be  seen 
in  the  photograph  (PI.  XIX,  fig.  1),  which  represents  a  typical  speci- 
men of  each.  The  results  of  measuring  23  specimens  of  O.  nanella 
and  34  of  0.  lamarckiana  are  seriated  in  the  form  of  curves  of  equal 
area  in  fig.  3.  It  will  be  observed  in  this  figure  that  not  only  are  the 
two  curves  quite  distinct,  but  that  they  are  separated  by  a  wide  gap. 
The  discontinuity  is  tremendously  in  excess  of  the  probable  errors, 
the  distance  between  the  means  of  the  two  curves  being  more  than 
forty  times  the  sum  of  the  probable  errors  of  the  means.  The  heights 
of  Onagra  nanella  group  themselves  about  the  mean  value  22.81  ±1 .02 
cm.,  with  a  range  from  7  cm.  to  35  cm.,  and  those  of  O.  lamarckiana 
about  the  mean  value  88.68  ±  0.55  cm.,  with  a  range  from  77  cm.  to 
96  cm.  The  other  constants  present  quite  as  interesting  differences. 
Although  the  mean  height  of  O.  nanella  is  only  one-fourth  as  great  as 
that  of  0.  lamarckiana,  the  standard  deviation,  <r,  is  considerably 
greater,  being  7.26  ±  0.72  cm.  in  the  former  and  only  4.76  ±  0.39  cm. 
in  the  latter.     As  the  mean  and  the  standard  deviation  are  combined 

in  the  formula   ^^,  to  form  the  coefficient  of  variability,  the  latter 

constant  shows  an  even  more  remarkable  difference  between  these  two 
forms  than  do  the  means.  The  coefficient  of  variability  in  the  height 
of  Onagra  nanella  is  notably  high,  31.84  ±  3.16  per  cent.,  while  that 
in  O.  lamarckiana  is  quite  as  notably  low,  5.37  ±  0.44  per  cent.  This 
is  particularly  interesting,  as  will  be  seen  later,  in  its  agreement  with 
the  fact  that  in  most  of  the  characters  chosen  for  this  study  the 
mutant  is  significantly  more  variable  than  the  parent-form. 

The  branching  habit  of  Onagra  rubrinervis. — The  nature  of  the 
branching  of  O.  rubrinervis  as  compared  with  that  of  0.  lamarck- 
iana is  such  as  to  give  it  a  very  characteristic  aspect.  On  the  average 
about  twice  as  many  of  the  axillary  buds  develop  branches  and  these 
branches  have  a  greater  average  length.  In  both  species  there  is  a 
whorl  of  long  lateral  branches  surrounding  the  base  of  the  main  axis. 
In  0 .  rubrinervis  the  central  axis  bears  numerous  branches  roughly 
correlated  with  their  position  on  the  axis  in  such  a  way  as  to  give  the 
plant  as  a  whole  a  distinctly  conical  form.  In  0.  lamarckiana,  on  the 
other  hand,  the  branches  arising  from  the  central  axis  are  less  numer- 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


39 


ous,  shorter,  and  evidently  less  closely  correlated  with  their  position 
on  the  axis,  but  show  a  tendency  to  group  themselves  somewhat  above 
the  base,  so  that  the  plant  resembles  the  framework  of  an  inverted 
umbrella.     (Cf.  PL  XIX,  fig.  i,  and  PL  XXI.) 


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MUTANTS   AND    HYBRIDS    OF    THE   OENOTHERAS. 


Although  such  a  character  as  this  is  too  largely  influenced  by  the 
individual  physiological  vigor  to  be  of  any  value  as  a  diagnostic  char- 
acter, the  difference  of  aspect  between  the  lots  of  plants  of  these  two 
species  was  so  striking  that  it  was  thought  interesting  to  give  it  quan- 
titative expression.  A  comparison  of  the  number  of  lateral  branches 
shows  complete  discontinuity  between  the  two  species  in  this  regard, 
the  range  in  O.  lamarckiana  being  from  n  to  25,  and  in  0.  rubrinervis 
from  34  to  62.  Curves  of  equal  area  representing  the  variation  in  the 
number  of  branches  of  17  specimens  of  0.  rubrinervis  and  of  20  speci- 
mens of  0.  lamarckiana  selected  by  lot,  are  shown  in  fig.  4.  The 
constants  of  these  curves  are  as  follows : 


Onagra  lamarckiana. 
Onagra  rubrinervis  . . 


M 


ean. 


Meters. 

20.70  ±  0.49 
42.35  ±  1.04 


Standard  deviation. 


Meters. 

324  ±  0.35 
6.34  ±  0.73 


Coefficient  of  variability. 


Per  cent. 

15.7  ±  1.7 
15.0  ±1.7 


If,  instead  of  the  number  of  branches,  we  consider  the  total  branch- 
length,  the  results  are  in  some  respects  more  striking  still,  for  in  gen- 
eral the  branches  are  longer  in  0.  rubrinervis  than  in  O.  lamarckiana. 
This  did  not  prove  invariably  true,  however,  and  the  discontinuity 
which  should  have  been  increased  by  this  difference  in  average  length 
is  lost  through  the  occurrence  of  a  specimen  of  0.  r ub rinervis  having 
a  total  branch-length  of  only  7.79  meters,  though  it  had  39  branches. 
This  is  well  within  the  range  of  total  branch-length  of  0.  lamarckiana, 
which  varied  in  this  respect  between  3.65  meters  and  8.41  meters. 
The  greatest  length  of  branches  observed  in  any  specimen  of  0.  rubri- 
nervis was  29.98  meters.  The  variability  in  regard  to  total  branch 
length  is  presented  graphically  in  fig.  5.  The  constants  of  these 
curves  are  as  follows  : 


Onagra   lamarckiana. 
Onagra    rubrinervis. . . 


M 


ean. 


Meters. 

6.68  ±  0.20 
18.19  ±  1.30! 


Standard  deviation. 


Meters. 

1.35  ±0.14 
7.95  ±;0.92 


Coefficient  of  variability. 


Per  cent. 

20.2  ±  2.2 
43.7  ±5.1 


This  comparison  shows  a  remarkable  difference  throughout,  the 
most  important  feature  probably  being  the  fact  that  the  coefficient  of 
variability  in  total  branch-length  is  more  than  twice  as  great  in  O. 
rubrinervis  as  in  0.  lamarckiana. 

The  size  and  shape  of  the  leaves  of  Onagra  rubrinervis, — Much 
more  important  taxonomically  than  stature  and  branching  are  the 
leaf-characters,  and  it  is  just  here  that  statistical  study  encounters  the 
most  serious  obstacles  in  seeking  a  satisfactory  basis.     In  the  first 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  41 


place,  some  of  the  leaf-characters  are]incapable"of  quantitative  expres- 
sion, such  as  the  degree  of  crinkling  of  the  leaf,  which  is  a  striking, 
though  not  an  absolutely  distinctive  feature  of  the  leaf  of  0.  lamarck- 
iana.    Some  leaves  of  O.  rtibrinervis  are  also  crinkled,  but  it  is  a  gen- 


70 


66 


m 


m 


60 


45 


40 


35 


:;o 


35 


20 


15 


10 


Fig.  5.  Variation  in  total  branch-length  of  Onagra  lamarckiana  and  O. 
rubrinervis.  O.  lamarckiana:  Range,  3.65  to  8.48  meters;  M.,  6.68  +  0.20 
meters;  <r,  1.85  ±  0.14  meters;  C.  V.,  20.2  ±  2.2  per  cent.  O.  rubrinervis: 
Range,  7.79  to  29.98  meters;  M.,  18.19  ±  1.30  meters;  a,  7.95 ±0.92  meters; 
C.  V.,  43.7  ±5.1  per  cent. 

eral  character  of  the  leaf  of  0.  lamarckiana  and  only  occasional  in 
0.  rubrinervis.  Other  characters,  although  measurable,  present  tech- 
nical difficulties  incommensurate  with  the  value  of  the  results,  as,  for 
instance,  leaf-thickness  and  degree  of  pubescence.     The  leaf  of  0. 


42 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


45 

50 


95 
100 


120     "  "145 
125  150 

Fig.  6.  Variation  in  leaf-length  of  Onagra 
lamarckiana  and  O.  rubrinervis.  O. 
lamarckiana  :  R.,49to  137  mni. ;  M.,96.85 
±  0.  42  mm. ;  o-,  13.08  ±  0.30  mm. ;  C.  V., 
13.60  ±  0.81  per  cent.  O.  rubrinervis  :  R., 
63  to  142  mm. ;  M.,  97.99  ±  0.34  mm. ;  o-,12.87 
±  0.24  mm. ;  C.  V.,  12.62  ±  0.24  per  cent . 


lamarckiana  is  noticeably  thicker 
than  that  of  0.  rubrinervis.  So- 
called  qualitative  differences  are 
usually  compounds  of  several  meas- 
urable characters,  any  one  of  which 
is  a  wholly  unsatisfactory  measure  of 
the  quality,  while  only  one,  two,  or 
several  at  most  of  these  measurable 
characters  can  be  dealt  with  mathe- 
matically at  a  time.  Leaf- form  is 
a  character  of  this  kind.  Not  only 
is  the  relation  of  length  to  breadth 
important,  but  the  relative  posi- 
tion of  the  widest  part  of  the  leaf, 
the  angles  of  apex  and  base,  and 
indeed  the  curvature  of  the  mar- 
gin at  every  point  from  petiole  to 
apex,  enter  as  essential  features  of 
leaf- form,  and  no  tangible  mathe- 
matical expression  can  be  devised 
to  represent  it.  Confining  ourselves 
to  a  single  measurable  character, 
such  as  leaf  length  or  breadth, 
there  is  still  another  difficulty  which 
must  be  met.  The  leaf  is  a  differen- 
tiated organ  and  there  is  no  exact 
homology  between  any  two  leaves. 
In  a  plant  which  has  but  few  leaves 
this  is  strikingly  evident,  and  no 
leaf  on  a  stem  which  has  ten  leaves 
corresponds  exactly  to  any  leaf  on 
another  plant  of  the  same  species 
which  carries  but  nine  leaves.  In 
plants  with  numerous  leaves,  as 
in  the  various  species  of  Onagra, 
the  degree  of  differentiation  between 
adjacent  leaves  is  so  slight  that 
they  may  be  treated  as  homotypic 
without  appreciable  error,  provided 
as  nearly  as  possible  the  corre- 
sponding parts  of  the  various  speci- 
mens are  used  as  the  source  of 
leaves  for  the  study. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


43 


The  leaves  chosen  for  this  comparative  study  were  taken  from  a 
point  about  two-fifths  of  the  distance  from  the  proximal  toward  the 
distal  end  of  the  long  lateral  branches  mentioned  above  as  forming 
a  whorl   about  the  base  of  the  main    axis.     The    number  of  such 
branches  borne  by  each  specimen   allowed  the  collection  of  a  suffi- 
ciently large  number  of  leaves  by  taking  them  from  a  very  short  sec- 
tion of  each  branch,  so 
that  the   error   due  to 
differentiation  is  insig- 
nificant compared  with 
the '  'chance'  'variation. 
From  20  to  30   leaves 
were  taken  from  each 
of  20  specimens  of  each 
species,  and  the  width, 
and  the  length  from  the 
base  of  the  petiole  to 
the  apex,  were   meas- 
ured in  the  fresh  con- 
dition. The  length  and 
width  were  then  com- 
bined for  each  leaf  in 
the    ratio,     width     -5- 
length,   this  being   the 
simplest    possible    ap- 
proximation to  a  sat- 
isfactory mathematical 
expression     for      leaf- 
form.       The    curves 
shown     in     figs.    6,    7 
and  8  compare  graph- 
ically   the     results    of 
these  measurements.  It 
will  be  noted  on  refer- 
ence to  fig.  6  that  the 
length    of    the    leaves 
in  the  two    species    is 
almost  identical,  while 
fig.   7  shows  that  with  respect  to  the  width  of  leaf  they  are  quite 
different,  though  not  discontinuous.     In  consequence  of  the  approxi- 
mate identity  in  leaf-length  the  ratio  representing  leaf- form  corresponds 
closely  with  the  leaf-width  in  the  character  and  degree  of  overlapping 
of  its  curves,  as  will  be  seen  on  comparing  figs.  7  and  8. 


Fig.  7.  Variation  in  leaf-width  of  Onagrarubrinervis  and 
O.  lamarckiana.  O.  rubrinervis:  R.,17  to  10mm.;  M  . 
29.736  ±  0.098  mm.;  <r,  3.589  ±  0.069  mm.;  C.  V.,  12.07  ±  0.28 
percent.  O.  lamarckiana  :  R.,  24  to  50  mm. ;  M.,  37.H17 
±  0.137  mm. ;  o-,  4.248  ±  0.097  mm. ;  C.  V.,  11.29  ±  0.26  per 
cent. 


44 


MUTANTS   AND    HYBRIDS    OF   THE   OENOTHERAS. 


The  constants  of  these  curves,  which  represent  the  variations    of 
the  two  populations,  each  taken  as  a  whole,  are  as  follows: 


Mean. 

Standard  deviation. 

Coefficient  of  variability. 

Variation  in  length  of  leaf : 

Onagra  lamarckiana  

Millimeters. 

96.15    +0.42 
97.99   ±0.34 

37.617  +  0.137 
29.736  ±  0.098 

Per  cent. 

39.964  +  0.123 
30.077  ±  0.084 

Millimeters. 
13.08    +0.30 
12.37    +0.24 

4.248  +  0.097 
3.589  +  0.069 

Per  cent. 
3.811  +  0.087 
3.098  +  0.056 

Per  cent. 

13.60  +  0.31 
12  62  +  0  24 

Variation  in  width  of  leaf : 

Onagra  lamarckiana 

11.29  +  0.26 
12  07+023 

Variation  in  the  ratio  between 
width  and  length: 

Onagra  lamarckiana  

9.53  +  0.22 
10  30  +  0  20 

Considering  the  great  variability  of  leaves,  it  would  not  be 
expected  that  two  species  so  closely  related  would  exhibit  complete 
discontinuity  in  size  of  leaf  or  in  the  ratio  between  width  and  length. 
It  is  not  so  much  the  extreme  types  of  leaves  which  give  to  a  plant  its 
characteristic  appearance  and  appeal  to  the  systematist,  as  the  type  to 
which  the  majority  of  the  leaves  belong.  The  mean  values  of  the 
various  leaf-characters  for  each  individual  would  much  more  nearly 
represent  the  conditions  as  seen  by  the  descriptive  botanist.  For  this 
reason  it  seemed  important  to  compare  the  means  of  length,  width, 
and  form  of  leaves  in  the  individual  plants  of  the  two  species.  The 
results  are  represented  in  figs.  9,  10,  and  11,  and  show  that  there  is 
approximate  identity  in  the  mean  length  of  the  leaf,  but  complete  dis- 
continuity in  both  mean  widths  and  the  mean  ratios  of  width  to  length. 
The  constants  were  not  determined  for  these  curves,  as  an  inspection 
of  the  curves  together  with  a  statement  of  the  ranges  will  sufficiently 
indicate  the  nature  and  degree  of  discontinuity  present. 

The  ranges  of  mean  values  of  the  leaf-characters  in  the  individ- 
ual plants  were  as  follows  : 


Length. 

Width. 

Width-=-length. 

Millimeters. 

88.42-112.32 
86.28-107.15 

Millimeters. 

33.74-41.64 
25.93-32.53 

Per  cent. 
34.62-44.41 
25  30  32  54 

It  will  be  noted  that  the  break  between  the  mean  values  of  leaf- 
width  and  that  between  the  mean  ratios  of  width  to  length  are  slight 
but  sufficient.  If  a  larger  number  of  specimens  had  been  used  the 
range  would  have  been  extended  somewhat  and  it  is  not  improbable 
that  they  would  overlap  some,  and  yet  the  unsatisfactory  character  of 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


45 


the  ratio  of  width  to  length  as  a  measure  of  leaf- form  would  not  allow 
us  to  infer  from  such  overlapping  that  the  two  species  are  not  abso- 
lutely distinct  with  respect  to  the  form  of  the  leaves.  This  fact  will 
become  convincingly  apparent  upon  reference  to  Plate  XXII,  in  which 


0  35  30  35  40  45        -  50  55 

Fig.  8.  Variation  in  ratio  of  width  to  length  in  the  leaves  of  Onagra 
rubrinervis  and  O.lamarckiana,  expressed  in  per  cents.  0-  rubrinervis: 
Range,  20-48;  M.,  30.077  ±0.084;  <r,  3.098 ±  0 .056 ;  C.  V.,  10.30  ±  0.20  per  cent. 
O.  lamarcUana:  Range,  28-53  ;  M..  S9.961  ±0.123;  <r,3.811  ±0.087;  C.  V., 
9.53  ±  0.22  per  cent. 

are  contrasted  the  leaves  from  the  specimen  of  0.  lamarckiana  having 
the  minimum  mean  ratio  and  those  of  the  specimen  of  0.  rubriiu 
having  the  maximum  mean  ratio.     According  to  this  statistical  meas- 


46 


MUTANTS   AND    HYBRIDS    OF    THE   OENOTHERAS. 


ure,  these  two  lots  of  leaves  are  the  most  nearly  identical  in  form  of  any 
two  plants,  belonging  to  these  two  species,  which  were  investigated. 
If  to  the  difference  of  outlines  as  shown  in  the  plate  could  be  added  the 
marked  crinkling  of  the  lamarckiana  leaves,  a  character  which  disap- 
pears on  pressing,  the  discontinuity  would  be  even  more  obvious. 

Interpretation  of  statistical  results. — In  reviewing  the  results  of  this 
study  one  feature  stands  out  prominently,  which  appears  to  the  writer 
to  be  of  more  fundamental  significance  than  the  mere  determination  of 
the  differences  in  superficial  characters  of  the  several  species  under 
consideration.  This  feature  will  be  apparent  upon  a  comparison  of 
the  coefficients  of  variability  throughout. 


A 

\     / 

\Yv 

^ 

^ 

/  \ 

'A 

^XA 

&§ 

/// 

/// 

. 

\ 

/ 

b 

k 

85-87   8S-90  91-93   94-96   97-99  100-102  103-105  106-108  109-111  112-114  115-117 


Fig.  9.  Variation  in  the  mean  length  of  leaves  in  Onagra  rubrinervis  and  O.  la- 
marckiana. Curve  for  O.  rubrinervis  shaded  with  lines  rising  to  the  right.  Range, 
O.  rubrinervis,  86.28  to  107.15  mm.  ;  O.  lamarckiana,  88.42  to  112.32  mm. 

The  variability  of  the  mutant  is  significantly  higher  than  that  of 
Onagra  lamarckiana  in  four  of  the  six  characters  considered.  In  the 
number  of  lateral  branches,  one  of  the  remaining  two  characters,  the 
excess  in  favor  of  0 .  lamarckiana  is  far  within  the  probable  error,  and 
therefore  has  no  significance.  Only  in  regard  to  the  leaf-length  of  0. 
rubrinervis  is  there  a  significantly  higher  variability  in  O.  lamarckiana 
than  in  its  mutant,  and  this  is  a  character  in  which  the  mutant  pre- 
sents no  material  difference  from  its  parent,  the  difference  between 
the  mean  lengths  of  leaves  in  the  two  species  being  only  i.i  mm.  in 
excess  of  the  sum  of  the  probable  errors. 

Probably  related  to  the  same  causes  which  determine  this  greater 
variability  of  the  mutants  is  the  fact  that  there  is  a  lower  degree  of 
correlation  between  the  length  and  breadth  of  the  leaves  of  0.  rubri- 
nervis than  in  0.  lamarckiana.    Correlation  tables  of  these  two  charac- 


MUTANTS    AND    HYBRIDS   OF   THE   OENOTHERAS. 


47 


ters  are  shown  in  figs.  12  and  13.  The  lesser  correlation  of  the  for- 
mer isapparent  to  the  eye  in  the  more  scattered  distribution  of  the 
variates.  The  coefficients  of  correlation  are  as  follows  :  Onagra  la- 
marckiana, 0.7916  ±  0.0090;  Onagra  rubrinervis,  0.6604  ±  0.0119. 
This  is  simply  another  way  of  expressing  the  fact  that  the  leaf-form  of 
O.  rubrinervis  is  more  variable  than  that  of  its  parent-species. 

If  increased  variability  and  decreased  correlation  be,  as  here  indi- 
cated, a  general  feature  of  those  characters  in  which  a  mutant  departs 
markedly  from  the  parental  condition,  how  is  it  to  be  interpreted?  It 
is  hinted  by  Weldon  ('02)  that  these  mutants  are  possibly  the  result  of 
selection  and  isolation.  No  one  can  deny  that  there  has  been  selec- 
tion and  isolation  in  their  culture,  but  it  may  be  questioned  whether 


35-26  27-28  29-30  31-32  33-34  35-36  37-38  3'J— 10  11-42 


Fig.  10.  Variation  in  the  mean  width  of  leaves  of  Onagra  rubrinervis  and  O. 
lamarckiana.  Curve  for  O.  rubrinervis  shaded  with  lines  rising to  the  right.  Kange : 
O.  rubrinervis,  25.93  to  32.53  mm.;  O.  lamarckiana,  33.71  to  41.64  mm. 

these  processes  have  been  carried  on  to  such  an  extent  as  to  explain 
the  peculiar  behavior  of  the  mutants  as  compared  with  that  of  an 
extreme  variate.  This  question  will  not  be  satisfactorily  answered 
until  a  newly  arisen  mutant  shall  be  subjected  to  various  conditions 
of  cross  and  self  fertilization,  and  the  results  are  studied  statistically. 
It  seems  fair  to  assume  that  there  has  been  a  more  discriminating 
selection  in  the  case  of  the  several  mutants  than  in  O.  lamarckiana.  It 
is  therefore  something  of  a  surprise,  if  Weldon's  suggestion  be  true, 
to  find  the  latter  less  variable  in  nearly  every  character  studied.  This 
surprise  is  due  to  what  may  be  a  false  assumption,  namely,  that  selec- 
tion necessarily  operates  to  lessen  variability.     Is  it  not  conceivable 


48 


MUTANTS   AND    HYBRIDS   OF   THE    OENOTHERAS. 


that  the  selection  of  an  extreme  condition  may  result  in  increased 
variability  even  after  several  generations  ? 

The  supposed  effects  of  self  and  cross  fertilization  can  hardly  be 
assumed  as  of  any  consequence  in  this  connection,  for  both  species 
have  been  self- fertilized  during  a  number  of  generations.  Just  what 
effect  this  has  had  upon  their  variability  is  not  known.  De  Vries 
does  not  think  that  cross-fertilization,  even  hybridization,  has  any 
appreciable  influence  on  the  frequency  of  origin  of  a  given  mutation 
in  a  mutating  species.  (De  Vries,  1901,  p.  211-212;   1903,  p.  425-426.) 


85-86    87-38    39-30    31-33    33-34    35-36    37-38    39-40    41-43    43-44 


Fig.  11.— Variation  in  the  mean  ratio  between  width  and  length  of  leaves  in 
Onagra  rubrinervis  and  O.  lamarckiana.  Curve  for  O.  rubrinervis  shaded 
with  lines  rising  to  the  right.  Range  :  O.  rubrinervis,  25.30  to  32.54  per  cent.;  O. 
lamarckiana,  34.62  to  44.41  per  cent. 

Weismann  (1892)  maintained  in  his  earlier  works  that  all  heredi- 
tary variation  is  due  to  cross-fertilization,  but  more  lately  he  has 
withdrawn  from  this  extreme  position,  and  now  considers  amphimixis 
"  nicht  alsdie  eigentliche  Wurzel  der  Variation  selbst,  denn  diese  kann 
unmbglich  auf  einen  blossen  Austausch  der  Ide,  sie  muss  vielmehr 
auf  einer  Veranderung  der  Ide  beruhen."  He  even  looks  upon  cross- 
fertilization  as  a  process  by  which  the  range  of  variation  is  lessened, 
and  the  variable  forms  which  he  thinks  may  arise  at  each  "  Neuanpas- 
sung,"  are  condensed  into  a  species  and  rendered  constant.  (Weis- 
mann, 1902,  2:235.) 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


49 


Darwin  performed  a  large  number  of  experiments  to  test  the 
effect  of  self  and  cross  fertilization,  but  his  object  was  to  determine  the 
advantages  or  disadvantages  as  measured  by  height,  productivity,  etc., 
rather  than  the  effect  on  variability.  The  number  of  specimens  used  by 
him  in  each  species  studied  was  hardly  sufficient  to  allow  conclusions 
of  value  regarding  variability ,  but  he  infers  that  variations  are  primarily 


X, 

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10 

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l 

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18 

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6 

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Fig.  12.    Correlation  table  of  length  and  width  of  leaf  in  Onagra  rubrinervis. 
Width  of  leaf  subject,  length  relative ;  p  =  0.6604  ±  0.0119. 


due  to  differences  of  environmental  conditions,  and  that  cross-fertiliza- 
tion tends  to  produce  uniformity  when  these  variations  are  slight,  and 
to  increase  the  diversity  when  the  variations  are  considerable.  These 
questions  need  thorough  reinvestigation,  and  their  discussion  is  futile 
until  such  investigation  is  made.      (Darwin,  1876,  p.  452.) 

If  the  Onagra  mutants  are  not  the  result  of  selection  and  isola- 
tion, acting  within  the  field  of  applicability  of  known  laws  of 
variation  and  heredity,  but  are  really,  as  they  have  been  called  by 
certain  German  writers,  ' '  correlation-breakers, ' '  may  not  the  increased 


50 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 


variability  and  decreased  correlation  be  explained  by  the  newness  of 
the  species,  which  may  be  assumed  to  want  that  perfect  adjustment  to 
their  surroundings  which  an  older  species  has  acquired  through  the 
cumulative  effects  of  long-continued  adaptive  reactions,  aided  by 
natural  selection — i.  e. ,  by  the  elimination  of  the  unadapted  ?     This 


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in 

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Fig.  13.  Correlation  table  of  length  and  width  of  leaf  in  Onagra 
lamarckiana.  Width  of  leaf  subject,  length  relative  ;  p  = 
0.7916  ±  0.0090. 

question  also  can  be  answered  only  by  experimentation  and  observa- 
tion continued  through  a  series  of  }'ears. 

It  appears  highly  desirable  that  the  statistical  study  of  O.  lamarck- 
iana and  its  mutants  should  be  continued  during  a  series  of  years, 
and  that  similar  studies  should  be  made  of  other  mutating  and  mutant 
species.  The  exact  status  of  the  mutants  with  regard  to  their  varia- 
bility and  capacity  for  self-maintenance  may  be  most  conclusively 
determined  by  the  use  of  the  methods  entailed  in  such  work. 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  51 

GENERAL  SUMMARY. 

A  brief  resumi  of  the  more  salient  features  of  the  foregoing 
paper  will  serve  to  emphasize  the  contributions  made  to  the  subject 
during  the  course  of  the  experimental  work  described. 

A  continuance  of  the  effort  to  trace  the  nativity  of  0.  lamarckiana 
has  resulted  in  the  discovery  of  records  and  specimens  that  appear 
fairly  conclusive  that  it  is  a  true  and  independent  species  native  to 
America,  although  the  matter  is  not  decided  with  the  finality  afforded 
by  living  specimens  observed  in  the  field.  That  this  species  has  re- 
mained unchanged  during  a  period  of  a  hundred  and  sixteen  years  is 
established  beyond  doubt,  and  renders  the  matter  of  its  nativity  of  com- 
paratively little  importance  as  to  the  standing  of  the  mutants  derived 
from  it.  Perhaps  no  plant  is  known  in  which  the  purity  of  the  strain 
has  been  so  critically  examined  as  Lamarck's  evening-primrose.  Some 
of  the  mutants  are  derivatives,  most  of  which  have  become  separated 
from  the  parent-form  by  the  acquisition  of  new  characters,  while  others 
are  of  a  retrogressive  character.  Many  of  the  new  unit-characters  dis- 
played are  not  known  in  any  of  the  other  members  of  the  natural  group, 
and  thus  may  not  be  regarded  as  degressive  acquisitions,  or  as  due  to 
the  retraction  of  a  retrogressive  step  taken  in  the  previous  history  of 
the  parent-species. 

The  material  used  as  O.  bie?inis  in  the  investigation  described  in 
Die  Mutationstheorie  proves  to  be  a  large-flowered  species,  which 
has  probably  been  known  to  many  workers  as  0.  biennis  grandiflora. 
The  uniformly  unilateral  character  of  the  cross  between  this  species  and 
0.  lamarckiana  (O.  lamarckianaX  O.  biennis  grandiflora)  which  was 
an  unitypic  hybrid  very  similar  to  the  poll  en -parent,  a  result  which  led 
De  Vries  to  the  conclusion  that  O.  lamarckiana  was  a  direct  derivative 
of  the  latter,  probably  by  mutation.  A  re-examination  of  the  evi- 
dence, however,  recalls  that  the  cross  with  muricata  was  similarly 
unilateral  to  the  latter  when  used  as  a  pollen-parent,  and  it  is  evident 
that  too  much  weight  must  not  be  given  to  the  conclusion  in  question 
until  confirmatory  evidence  is  obtained. 

A  consideration  of  the  groupings  of  characters  leads  to  the  con- 
clusion that  O.  grandiflora  Ait.,  0.  lamarckiana  Ser.,  and  O.argiUi- 
cola  MacKenzie  are  much  more  closely  related  to  one  another  by  ana- 
tomical characters  and  physiological  traits  than  to  biennis  or  any 
other  member  of  the  genus.  Furthermore,  the  ranges  of  the  three 
species  mentioned  appear  to  be  more  or  less  identical,  or  overlapping. 

O.  grandiflora  Ait.  had  been  seen  by  but  few  botanists  in  a  living 
condition  in  America,  and  its  place  in  the  American  flora  had  become 


52  MUTANTS   AND    HYBRIDS    OF    THE   OENOTHERAS. 

a  matter  of  much  doubt,  but  field  expeditions  guided  by  descriptions 
from  Bartram's  travels  in  1776  resulted  in  a  rediscovery  of  the  species 
in  a  spot  not  far  from  the  original  locality.  This  found,  the  confusion 
which  had  arisen  as  to  the  separation  of  this  species  and  0.  lamarck- 
iana  is  cleared  up. 

The  cultures  of  the  evening-primroses  made  in  the  New  York 
Botanical  Garden  show  that  two  or  more  elementary  species  are 
grouped  under  some  of  the  specific  names  as  ordinarily  accepted. 
The  failure  to  recognize  these  elements  has  resulted  in  the  prevalent 
opinions  as  to  the  wide  range  of  fluctuating  variability  exhibited  by 
these  plants.  This  is  especially  true  of  O.  biennis ,  which  has  enjoyed 
a  reputation  for  variation  not  justifiable  by  systematic  and  orderly 
observations  made  on  plants  grown  under  various  conditions.  One  of 
the  forms,  apparently  typical  of  the  true  O.  biennis  now  under  culti- 
vation, is  in  a  mutative  condition,  but  description  of  the  derivatives 
is  reserved  until  they  have  completed  a  cycle  of  development. 

O.  cruciata  as  it  exists  at  the  present  time  in  the  cultures  in  the 
New  York  Botanical  Garden,  and  in  the  Botanical  Garden  of  Amster- 
dam is  composed  of  three  elementary  species,  which  are  fairly  distinct 
and  without  intergrading  forms.  A  careful  analysis  of  the  occurrence 
of  the  group  leads  to  the  inevitable  conclusion  that  one  of  the  forms 
is  in  a  mutating  condition. 

It  is  evident  that  in  the  investigations  of  native  species  for 
possible  mutating  forms,  the  first  and  most  important  task  to  be 
completed  is  that  of  the  resolution  of  the  forms  selected  into  their 
elementary  constituents.  Otherwise  the  seed  obtained  from  plants 
belonging  to  separate  strains  might  well  give  an  appearance  of 
variability  not  justifiable  by  the  facts.  Mutations,  therefore,  may  be 
taken  as  properly  authenticated  only  when  appearing  in  guarded 
pedigree-cultures  from  seeds  produced  by  a  known  individual,  which 
should  be  preserved  for  comparison.  Discussions  of  mutants  secured 
under  other  conditions  may  serve  an  important  purpose  in  offering 
clues  which  will  be  useful  in  the  selection  of  research  material,  but 
can  have  no  direct  or  actual  value  as  a  contribution  to  the  subject. 

The  evening-primroses  of  eastern  North  America,  from  which 
probably  all  of  the  forms  cultivated  in  Europe  are  derived,  may  be 
divided  into  two  groups — a  group  including  O.  biennis,  muricata, 
octkesiana,  and  cruciata,  in  which  the  flowers  are  comparatively  small, 
and  in  which  self-pollination  is  possible  and  frequent.  The  second 
group,  including  species  native  to  a  region  farther  south,  comprises  0. 
argillicola,  0.  grandiflora,  and  O.  lamarckiana ,  in  which  the  flowers  are 
large  and  the  stamens  are  much  shorter  than  the  pistil,  a  condition 
which  with  some  accessory  structures  favors  cross -pollination. 


MUTANTS   AND    HYBRIDS   OF    THE   OENOTHERAS.  53 

The  hybrid  O.  lamarckiana  X  O.  cruciata  consisted  of  a  single 
type  in  which  the  characters  of  the  pollen-parent  were  largely  domi- 
nant, although  none  of  them  were  transmitted  unchanged.  A  singu- 
lar union  of  characters  was  shown  in  the  relative  lengths  of  the  sta- 
mens and  pistils,  a  feature  favoring  cross  and  self  fertilization.  Some 
of  the  flowers  bore  stamens  shorter  than  the  pistils,  while  in  others 
these  organs  were  of  equal  length.  Many  of  the  modifications  of  the 
predominating  characters  were  dependent  upon  and  were  modified  by 
the  alterations  in  the  general  stature  of  the  plant.  This  hybrid  corre- 
sponds quite  closely  with  the  descriptions  of  0.  cruciata  varza,  a 
supposed  hybrid  of  0.  cruciata  and  0.  muricata  given  by  De  Vries. 

The  hybrid  of  0.  lamarckiana  X  0.  biennis  was  of  a  pleiotypic 
character,  being  composed  of  four  well-differentiated  types  with  no  inter- 
grading  forms.  This  result  differs  widely  from  that  obtained  by  De 
Vries  in  hybrids  with  0.  biennis  grandiilora  and  0.  muricata  as  the 
pollen-parent.  In  both  of  the  last-named  instances  the  result  of  the 
cross  was  a  unitypic  hybrid  closely  unilateral  to  the  pollen-parent. 
In  0.  lamarckiana  X  0.  biennis  some  characters  of  both  parents  were 
transmitted  to  all  of  the  four  types  of  the  hybrid,  but  the  greater  num- 
ber of  the  active  characters  were  those  of  the  pollen-parent. 

A  remarkable  predisposition  or  weakness  to  the  attack  of  a 
fungal  parasite  was  exhibited  by  one  of  the  types.  The  habit  of  ine- 
quality of  growth  of  the  laminae  resulting  in  crinkling,  characteristic 
of  lamarckiana,  was  transmitted  to  all  individuals  of  the  four  types  of 
the  hybrid.  The  symmetrical  form  of  the  terminal  rosettes  of  lamarck- 
iana was  transmitted  unchanged  to  two  of  the  types.  No  other  char- 
acters of  the  pistil-parent  were  inherited  in  their  entirety,  although  a 
number  of  qualities,  approximating  those  of  lamarckiana  sufficiently  to 
be  termed  "  dominant"  by  some  authors,  were  seen.  Three  of  the 
types  were  goneoclinic  to  the  pollen-parent,  while  the  fourth  (No.  2.24) 
may  be  fairly  taken  as  furnishing  an  example  of  an  intermediate  form,  so 
far  as  such  estimations  may  be  taken  to  be  of  value.  The  zigzag  stem, 
No.  2.27,  is  an  example  of  the  dominancy  of  a  feature  usually  latent  in 
the  pistil-parent,  but  exhibited  by  one  of  its  mutants,  rubrinervis.  The 
capacity  for  self-fertilization  was  dominant  in  three  of  the  types,  but 
in  the  fourth  a  variability  between  cross  and  self  fertilization  was 
indicated  by  the  varying  relative  lengths  of  the  stamens  and  pistils .  It 
is  to  be  noted  in  this  connection  t'iat  0.  brcvistylis,  one  of  the  mutants 
of  0.  lamarckiana  Mas  a  pistil  shoiierthan  its  stamens,  and  is  therefore 
adapted  to  self-fertilization,  although  no  actual  physiological  predis- 
position in  the  matter  is  found. 


54  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

The  recurrence  of  known  mutants  of  0.  lamarckianawas  observed. 
O.  mbrinervis  appeared  among  the  hybrid  progeny  of  O.  lamarck- 
iana X  0.  biennis,  in  which  imperfect  castration  had  been  accomplished 
and  the  parental  strain  appeared  in  the  cultures.  It  appears  therefore 
that  the  mutant  may  be  considered  as  a  derivative  of  the  one  parent 
purely,  although  the  possibility  is  not  excluded  that  it  might  have  come 
as  a  hybrid  strain,  as  has  been  observed  by  De  Vries  in  several  crosses. 
Better  authenticated  mutants  were  seen  to  arise  from  seeds  obtained 
from  purely  fertilized  plants  of  O.  lamarckiana  grown  in  the  botanical 
garden  at  Amsterdam  in  igoi  ;  also  from  seeds  of  the  same  species 
gathered  in  the  New  York  Botanical  Garden  in  1903  after  similar 
precautions  had  been  observed.  0.  albida , 'scintillans ,  gigas,  oblonga, 
subovata,  and  O.elliptica  were  found  among  the  mutants,  offering  evi- 
dence of  the  indubitable  occurrence  of  the  mutants  in  purely  fertilized 
seeds,  and  also  that  O.  lamarckiana  has  not  reached  the  end  of  its 
mutative  period.  Furthermore,  seven  forms  not  definitely  assignable 
to  any  of  the  known  mutants  of  this  parent  were  found,  showing  that 
the  range  of  the  mutability  of  the  species  had  been  extended  by 
unknown  causes,  but  which  were  included  in  an  environment  of 
cultural  conditions  extremely  favorable  to  rapid  and  vigorous  growth 
and  development.  It  seems  safe  to  assume,  therefore,  that  mutation 
is  induced,  or  at  least  increased,  by  favorable,  not  adverse  conditions, 
though  the  duration  of  the  experiments  has  not  been  sufficient  to 
permit  an  analysis  of  this  phase  of  the  subject. 

0.  gigas,  the  species  most  recently  tested  in  the  mutation -cultures 
in  New  York,  was  seen  to  agree  in  stature  and  habit  with  the  indi- 
viduals grown  in  the  original  locality  at  Amsterdam.  Only  about 
half  of  the  individuals  could  be  brought  into  bloom  during  the  first 
season,  although  it  was  extended  to  ten  months  by  special  methods  of 
culture — a  fact  in  accord  with  the  behavior  of  the  plant  in  De  Vries 's 
cultures.  The  constancy  of  the  species  also  extends  to  its  variability 
as  to  the  forms  of  the  leaves,  an'attribute  also  previously  recognized. 

The  results  of  the  statistical  studies  show  that  some  of  the  unit- 
characters  of  the  mutants  have  a  much  greater  variability  than  the 
corresponding  features  of  the  parent-form,  and  the  greater  amplitude 
of  the  fluctuations  is  coupled  with  a  decreased  correlation. 

Thus  the  coefficient  of  variability  of  the  height  of  the  shoot  of 
7ianella  is  31.84  ±  3.16  percent,  while  that  of  lamarckiana  is  5.37 db 
0.44  per  cent.  The  coefficient  of  variability  for  the  number  of  branches 
of  mbrinervis  is  15.0  zfc  1.7  per  cent,  and  for  the  total  length  of  the 
branches  is  43.7  =k  5.1  per  cent,  and  for  the  ratio  between  width  and 
length  of  the  leaves  is  10.30  ±  0.20  per  cent ;    for  the  number  of 


MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS.  55 

branches  of  lamarckiana  15.7  ±  1.7  per  cent,  for  the  total  length  of  the 
branches  20.2  ±  2.2  per  cent,  and  for  the  ratio  between  the  width 
and  length  of  the  leaves  9.53  =b  0.22  per  cent. 

The  great  variability  of  the  mutants  does  not,  however,  seem  to 
result  in  any  diminution  of  the  gap  that  separates  them  from  the 
parent  form,  and  no  movement  in  this  direction  has  been  observed  in 
the  long  period  which  has  elapsed  since  the  new  species  came  into 
existence.  Thus  the  heights  of  0.  nanella  group  themselves  about  the 
mean  value  of  22.81  d=  1.02  cm.,  with  a  range  from  7  to  35  cm.,  while 
those  of  0.  lamarckiana  group  themselves  about  the  mean  of  88.68  dz 
0.55  cm.,  with  a  range  from  77  to  96  cm.  The  number  of  branches 
per  individual  of  lamarckiana  ranged  from  n  to  25,  while  that  of 
rubrinervis  was  34  to  62.  The  actual  discontinuity  is  somewhat  more 
fully  expressed,  however,  by  a  comparison  of  the  numerous  features 
which  elude  measurements  to  be  seen  in  Plate  XXII,  in  which  leaves 
from  the  specimens  of  lamarckiana  and  rubrinervis  which  approached 
each  other  most  nearly  are  shown.  The  actual  discontinuity  between 
the  retrograde  variety,  0.  nanella,  and  its  parent  in  the  leading  feature 
of  height  of  stem  is  even  more  marked  than  the  gap  between  the 
various  unit-characters  of  rubrinervis  and  lamarckiana. 

Recurring  again  to  the  amplitude  of  the  fluctuations  in  the 
mutants,  it  is  to  be  said  that  it  is  doubtless  much  greater  in  the  leaf- 
forms  of  the  retrograde  variety,  0.  nanella,  than  in  any  which  have  been 
measured,  if  the  entire  mass  of  foliage  is  taken  into  account,  since  in  a 
certain  mid-stage  in  the  rosette  it  is  practically  impossible  to  distinguish 
it  from  the  parent,  although  fully  distinct  as  to  form  and  size  of  the 
leaves  in  the  very  young  and  very  old  rosettes.  The  very  range  of 
variation  may  be  in  itself  a  character  of  the  mutants,  in  which  case  no 
reason  could  be  given  for  its  existence,  any  more  than  reasons  could  be 
given  for  the  existence  of  any  other  unit-character.  Similar  diffi- 
culties might  be  encountered  in  seeking  an  explanation  of  the  com- 
parative amplitude  of  variation  of  any  group  of  related  forms. 


56  MUTANTS   AND    HYBRIDS   OF   THE   OENOTHERAS. 

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